PROSANTA CHAKRABARTY

EXPLAINING LIFE

Through Evolution

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Intro to Indian Edition

There is a beautiful Sanskrit word, ‘ayurveda’ that translates in English to ‘the science of life’.¹ Although generally relating to human health or homeopathic medicine, I’d like to see the shift of the usage of ayurveda to its literal translation as perhaps an enlightened synonym of ‘biology’, ‘élan vital’ or perhaps of ‘evolution’. It is a term that makes me think of how words and phrases can have different meanings for different people and how words too can evolve. Even the word ‘evolution’ evolved in Charles Darwin’s time from a meaning closer to ‘development’ (in the sense of a developing embryo) to its current definition, essentially the accumulation of heritable changes in organisms that can lead to the formation of new species from ancestral forms.

Interestingly, Darwin and others instead used the now obsolete word ‘transmutation’, which then meant something closer to our current definition of ‘evolution’.² Over time, the meanings of words can change, but previous usages remain part of their history, just like species can retain the historical features of their ancestors. Except in biology, modifications often lead to entirely new species, so perhaps if we changed ‘ayurveda’ to ‘ayurvedology’ we’d have a better fit with the evolution analogy.

When Premanka Goswami approached me about publishing with Penguin Random House India, I got a bit nervous about the thought of publishing for an Indian audience. Born and raised in North America, I know India as my ancestral homeland, the birthplace of my parents, grandparents, great-grandparents and ancestors back to time immemorial, yet I still view India through the lens of a stranger. I am part of the Indian diaspora, but perhaps the part that sometimes feels adrift, distant and disconnected from the motherland. My name, my facial features, my skin tone, all divulge my Indian heritage to North Americans. But my accent, my mannerisms, my experiences are all American—I own that duality, but often fumble the consolidation (e.g., I eat samosas with a fork and barbecue sauce). Throughout this Indian edition you will see a bit of both sides of me, but hopefully my scientific perspectives will translate no matter what flavour of human you are. What does it even mean to be ‘Indian’ in the biological sense . . .? Well, read on, we will get to that (see Figure 1). And if you are not ‘Indian’, no worries, this is a book about evolution and life, and you don’t need to be an ayurvedologist to understand it.

Figure 1: My ancestry test results. The percentages are real (taken with a grain of salt), the historical figures I’ve assigned are a fiction of who I’d like to be descended from. Yul Brynner is representing his ‘King of Siam’ character not himself (he pretended to be Swiss/Japanese but had mostly Russian ancestry). Alexander the Great left no direct line (his son was killed before having his own children) and although every Asian thinks they have some Genghis Khan in them, we won’t know without some DNA link to his actual descendants—which we don’t have.

PART I

A Personal Prologue

Called to Action

In 2008, the year I moved to the state, the Louisiana Science Education Act was passed with the backing of the then governor, Bobby Jindal. The name of the law is misleading, as it allowed schools in Louisiana to teach the Biblical account of creation in science classes as an alternative to evolution.¹ Jindal went as far as to say that local schools should determine how science is taught in classrooms.² That meant that if the local public school’s science teacher wanted to teach that all living land animals were the descendants of creatures carried on Noah’s Ark, then well, that was just fine with the governor and the supporters of the law.

At the time, I presumed that Bobby Jindal (born Piyush Jindal) was probably a smart person who was somehow misled. I jokingly called him ‘my uncle Bobby’ because as an Indian person I could claim all other Indians as kin, and maybe saying the governor was a relative could get me out of a speeding ticket (it couldn’t). My Uncle Bobby should have known better than to pass anti-evolution legislation. He was, after all, someone who held a Biology degree from Brown University and a Rhodes Scholar (but going to an Ivy League school and Oxford doesn’t necessarily make you smart, just educated). Part of the reason he promoted this law was to pander to the so-called ‘religious right’. At the very least, he knew that the law was illegal because of the ‘separation of church and state’ clauses of the First Amendment of the US Constitution. He did know this, and he ignored it.*

So what’s the big deal anyway? Well, you just don’t teach your own religious views in a public science class. Science is about observing and testing natural phenomena in order to give a reasoned, evidence-based explanations for those events. Religion, on the other hand, can provide answers to questions science doesn’t cover (e.g., what is the meaning of life?) but it can also provide answers that can’t always be tested. For instance, let’s say your answer to why apples drop to the ground when they fall out of a tree is ‘God made it happen’; that isn’t something I can prove false, because I can’t test it. There isn’t room for questioning things or scientific inquiry if you believe flatly that ‘God controls everything that happens’.

The other problem with teaching religion in a science class is that there are many religions with a variety of beliefs. Faith-based beliefs about creation differ by your religious persuasion. In one version of the Hindu creation myth, the Earth was part of the lotus flower that grew from the navel of Vishnu, and then the world was populated by Brahma and will be destroyed by Shiva.³ If I taught that version of creation as the truth in my science class, I wouldn’t last very long as a teacher. However, maybe this religious take would do well in the so-called ‘Indian Science Congress’, especially among participants pushing fringe Hindutva ideas that take some religious ideas literally (e.g., Brahma discovered dinosaurs).⁴

The problem again with the teaching ‘God controls everything’ is that you can’t prove or disprove it. In order to respond to a ‘Noah’s flood’ scenario I say, ‘There is no boat that can fit a pair of all living land animals, and having just a pair of each species wouldn’t provide enough genetic variability to restock the Earth; also it can’t rain for 40 days and 40 nights worldwide because we have a finite amount of water on Earth; and also all the freshwater animals would go extinct as they would be inundated by salty marine water; and where did all that water go afterwards? And there is no evidence of a huge worldwide flood from a few thousand years ago…’ The reply is just always, ‘God did it, so anything is possible.’ Well, I guess that would be the end of the conversation. ‘God did it’ can be your go-to answer, and that is fine. I am not here to judge or tell you how to live. My only issue is using that explanation to shutdown scientific discourse in an academic setting.

Science is all about testing explanations of natural phenomena to see if they hold up to rigorous testing. If you can explain everything away with ‘God did it and controls everything’, what’s the point of the testing? What’s the point of school? What’s the point of curiosity?

Religions ask for your faith in explaining the untestable and unprovable; science is here to help explain the rest by making testable predictions. However, does science require some faith? Yes, I would say. You have to believe that the results and observations you make are based in reality and that the results are the outcomes of predictable phenomena. (This idea dates back before Aristotle but is explicit in the writings of religious philosophers such as Albertus Magnus, Thomas Aquinas, Roger Bacon, Avicenna, Averroes and surely many others in every culture/religion/region.) If a deity changed and influenced every scientific experiment on a whim so that we couldn’t make predictions and the laws of physics were not immutable, then frankly, we wouldn’t be able to explain our universe with any scientific investigations. However, that latter scenario isn’t the case. We scientists can have faith in the fact that what we observe is an unmanipulated reality because our inquiries yield consistent and reliable results that allow us to reveal the secrets of our planet and of our universe ever more exactly. To paraphrase Galileo, ‘Religion shows the way to go to heaven, not the way the heavens go.’

Some would argue that there is room for studying nature in the slightly different religious take of ‘God started everything and made the rules’. That is, you can study the rules (e.g., gravity, evolution) and their consequences, without having to determine the origination of those rules. This playbook suits the ‘non-overlapping magisteria’ Stephen Jay Gould describes in his book Rocks of Ages.⁵ In that book, Gould argues that science and religion can complement each other without interfering with one another, as it does for many. I would perhaps state it more plainly as, ‘Science should not be anti-religion; and religion should not be anti-science.’ There is certainly room for compromise, and improved ‘cultural competency’ on both sides.⁶

That anti-evolution law is still on the books in my state. I don’t mean to pick on Louisiana—I genuinely love the state and am proud to call it my adopted home. My kids were born in Baton Rouge, and I’ve lived here for more than ten years. Louisiana isn’t the only state with issues over the teaching of evolution. In Alabama, biology textbooks include a disclaimer sticker warning you about the ‘theory of evolution’.⁷ In 2018, Arizona briefly had all references to the word ‘evolution’ deleted from the state’s science education standards.⁸ It isn’t just the so-called conservative states; I’ve met anti-evolution people in liberal Ann Arbor (where I obtained my PhD in evolutionary biology) and New York City (where I grew up). In fact, one in five high school teachers in the US teach creationism along with evolution in their classes (many teach it as the preferred scientific alternative).⁹ It isn’t just the US either—only 26% of people in Afghanistan accept human evolution,¹⁰ and in 2017 Turkey removed references to evolution from its textbooks.¹¹ Notably, the US ranks near Turkey in terms of how human evolution is accepted by the general public.¹² Indians appear to be much more accepting of evolution and science despite also being deeply religious.¹³

Again, I’m here with no other motive but to explain the scientific facts that are available. The science is why the vast majority of people who understand those facts accept evolution. I’m not here to challenge your beliefs—we all have our own truths. We get to pick our own beliefs, but we don’t get to pick our own facts. I’m here to help you better understand how science explains the origin of our species and of all life on Earth.

In discussions with many people who actually accepted evolution and science, I came to realize that a good percentage of them didn’t really understand the science of evolution. They just accepted evolution as fact because they trust science. They may understand even less than some people who don’t accept evolution because those people don’t trust science or may see some conflict with their religion. I want to help more people on both sides to understand evolution, so that hopefully it will be less divisive. (I think difficult subjects, like politics, are so acrimonious because no one really knows what they are talking about.) It is ultimately up to you to accept scientific facts (or not), and to convince yourself of whatever ‘truth’ you are willing to acknowledge.

Evolution isn’t the easiest topic to understand—nor the hardest either (‘It ain’t rocket surgery’, as they say), but it is easy to misinterpret, and it is often portrayed incorrectly. For instance, evolution is often depicted as something like the ‘March to Progress/Road to Homo sapiens’ mural by Randolph Franz Zallinger (Figure 2A), but that is very wrong. This image is often interpreted as presenting evolution as a progressive force making life more ‘complex’ or ‘perfect’, and that we (humans) are the most complex and perfect forms of life—we are not, there is no such thing and there is no way to objectively measure ‘complexity’ or ‘perfection’. Evolution isn’t goal-oriented or progressive. This mischaracterization led one Louisiana state senator to ask, ‘They evolved into a person?’¹⁴ when told of a long-term evolution experiment on bacteria. That experiment, actually called the LTEE (Long-term evolution experiment) provided a surprising example of an evolutionary adaptation observed as it occurred.¹⁵ That experiment in the lab of Dr. Richard Lenski found that some E. coli populations (from over 70,000 generations), all captive reared from the same source population, had evolved an adaptive trait.** ¹⁵–¹⁷ That is very clear evidence of evolution (e.g., change in the inherited characteristics of a population). What that state senator believed, based on that common misunderstanding of evolution, was that the only definitive evidence of evolution from that experiment would be if the bacteria turned into humans. Even given an infinite number of generations reared in those lab conditions, those bacteria would never turn into humans—that’s not how evolution works. I hope this book help explains how it does work (Figures 2B and 2C).

This book is not meant to preach to the converted, but rather to explain this topic to anyone with an open mind to learning. It is also meant to be a tool to aid those who themselves want to explain the topic to others.

Figure 2A: The most widely-used image for depicting evolution is wrong. This top figure gives the impression to many that we transformed from a monkey, then a chimp and a ‘caveman’ in a direct series leading to ‘modern man’. In reality, we share common ancestry with these other forms, but we did not progress from them—rather, we progressed with them from those shared ancestors. This image (2A) has done far more harm than good to those trying to better explain evolution. These depictions are based on the original ‘March of Progress/Road to Homo sapiens’ by muralist Rudolph Franz Zallinger.

Figure 2B: A more accurate way of depicting evolution is with a phylogenetic tree (an evolutionary branching diagram showing the links between closest relatives). The branches bifurcate (split in two), and those pairs sharing a ‘node’ (the point where the branches connect) are more closely related to each other. Here the tailed monkey is the closest relative to the five other primates—not the ‘ancestor’. The ancestors are represented in the nodes. Node ‘1’ is the common ancestor of the six primates (including humans) depicted above, node ‘2’ is the common ancestor of chimps + modern humans + extinct human species.

Figure 2C: After noticing that ‘#evolution’ on Twitter had nothing to do with biological evolution, I challenged people to tweet about evolution using that hashtag. My brilliant friend, Dr. John McCormack (@LAevolving on Twitter) came up with this emoji-based explanation (i.e., ‘phylomoji’) that helps illustrate the different meanings and interpretations of Figures 2A and 2B.

Pulled into the Fight

After that 2018 anti-evolution law was passed, many scientists in Louisiana decided to do something about it. Dr. Barbara Forrest, a philosophy professor at Southeastern Louisiana University, led the charge among academics to fight the good fight against the creationist movement that was trying to set up anti-evolution laws all over the country (see her co-authored book, Creationism’s Trojan Horse: The Wedge of Intelligent Design¹). The most well-known spokesperson against the creationists was a Louisiana high school student at the time, Zach Kopplin.² If Dr. Forrest was exposing the Trojan horse for what it was, Zach was Hector, the young prince out to take down Achilles. Zach made national news by making articulate arguments defending evolution and science. At my institution, Louisiana State University (LSU), my colleagues Dr. Christopher Austin, Dr. Bryan Carstens and others worked hard to make Evolution a core course for anyone majoring in Biology. A core course means all Biology majors are required to take it, something that Bobby Jindal didn’t have to do at Brown. Perhaps if Bobby had learned evolution in college, he wouldn’t have been moved to put the law in place. After Evolution became a core course, I decided to step up and teach it myself. The fight of my colleagues became my fight, and I thank them for letting me join the cause. We now teach evolution to several hundred students a semester at LSU.

Despite teaching a class on evolution and sometimes being asked to explain evolution on panels or seminars, I never thought of myself as an advocate for science education. I didn’t see the need—I thought that most people who were anti-evolution were just poorly informed, or so I assumed. It took me a while to realize that I wasn’t in a position to make that assumption. While prepping for a talk on evolution for the 2018 TED conference, I came to recognize that I usually talked to other biologists or biology majors about evolution, i.e., I was talking to people who already had a fairly good understanding of the fundamentals of biology; not so with the people helping prep my talk (who were experts in public speaking and other subjects, but not biologists). That was probably why I didn’t think evolution was such a complicated subject, but I was wrong. It only seemed like an intuitive subject to me because of how long I had been studying and thinking about it.

The early versions of my public evolution talks were often very jokey with lots of why-the-human-body-stinks jokes (e.g., in insult-comic Don Rickles’s voice: ‘Yeah, hang your baby-making soft bits on the outside of your body between your legs, where they will be easy to bump against a table—good idea!’) but I realized (with the help of more mature people) that insulting the human body isn’t the best way to explain why we aren’t the pinnacle of evolution (but read on—examples ahead). Instead, I decided to focus on how some of the most typical depictions of evolution are misleading and how so many people lack a fundamental understanding of what evolution is and where the facts and theories came from. I want to make evolution more accessible, and that’s why I wanted to write this book—to help people decide for themselves.

My own family helped to get me thinking about evolution from a different perspective than just as a mild-mannered professor. I have identical twins: every evolutionary biologist should have identical twins. My ten-year-old set, Chaya and Anjali, are very different from each other. I think often about evolution and how their identical genomes are reflected in their bodies and behaviours. I’m glad my wife kept me from carrying out my experiments of nature versus nurture on these clones (you know, only sending one to school, only hugging the other, etc.). Instead, we are doing a ‘common garden’ experiment, raising them in the same environmental conditions and seeing how they still end up different and distinct.* Obviously, I’m joking . . . sort of. But if I was pushed into science advocacy, it was for them. I want them to grow up in a more scientifically literate society.

Since I’m asking you to be interested in evolution, it may be worth explaining how I first became interested. I was first introduced to the topic formally by Bob Carroll at McGill University—at least the fun macroevolution bits (e.g., dinosaurs and mass extinctions). His funny and inspired lectures were a big part of me wanting to teach evolution myself one day. Sadly, Bob died of COVID-19 related complications in April 2020. One of the guest speakers Dr. Carroll brought in while I was at McGill was Steven Jay Gould, perhaps the most inspirational evolutionary biologist of the last fifty years. Learning that Gould was raised in Bayside, Queens, like myself, probably didn’t play an insignificant role in my continued interest in evolutionary biology.

My first hands-on work on evolution was related to describing a new species of fish while working as an undergrad at the American Museum of Natural History. What I learned then under the tutelage of Dr. Melanie Stiassny was not just taxonomy but a love of anatomy and ichthyology. In grad school in a department of evolutionary biologists at the University of Michigan, I was inspired daily to study evolution and phylogenetics (the study of the relationships on the Tree of Life). Dr. Douglas Futuyma, who wrote the most important textbooks on evolution (called Evolution—so I joke he literally wrote the book on evolution), helped me think about the nitty-gritty of the study of life on Earth, particularly at the microevolutionary, population level. I was also lucky enough to be an assistant teaching a short course during a theme semester at the University of Michigan called ‘Explore Evolution’. In that semester, I saw some of the best evolutionary biology speakers, including Svante Pääbo (who sequenced the Neanderthal genome and figured out that certain genes that could put you at greater risk of severe COVID-19 symptoms were inherited from Neanderthals³), Richard Lewontin** (who brought a mathematical influence to population genetic theory) and Eugenie Scott (who exposed the anti-evolution movement’s hidden agendas⁴). Being able to help teach evolution to undergrads that first time was eye opening. Few of those undergrads had any exposure to the science of evolution to that point, and they had few resources to help them learn on their own. I was privileged in having had those resources and mentors.

Now at LSU, I understand the impact of explaining evolution not just each time I teach my class but whenever I get an email or social media comment about my public talks. (I’m sure I’ll get a few more after this book comes out.) I’ve been called some pretty horrid things by some anti-evolution folks who don’t care to understand the science. They also don’t understand that I’m just presenting the best available knowledge on the subject, something lots of other people are also doing. I’m just trying to make the subject a little more approachable for everyone.

On Trust

The first time I was taught evolution I was in eighth grade, at Marie Curie Middle School 158 in Queens, New York, when I was about thirteen years old. The teacher said, ‘I’m going to talk about evolution for a moment, I apologize in advance to those of you who are religious . . .’ I don’t actually remember what he said next, something about human fossils from Africa, but that was it. Why the disclaimer? Was he saying something false? Unproven? Was it different from the Earth Science he taught us about continents and glaciers? If I could go back in time, I would raise my hand and ask, ‘Does every teacher have to apologize for teaching me science?’ Except I wouldn’t. I loved that teacher, and I know that he and most others aren’t trained to teach evolution, and that many people, even biology majors, aren’t exposed to it.*¹,²

Now I’m the teacher, and I know all too well why people approach the subject of evolution with trepidation. I occasionally get strange looks from people when I tell them what I teach in Louisiana. People sometimes comment that they have visions of kids throwing holy water on me, screaming at me while I read with my head down from a piece of paper behind some protective glass (a common but false stereotype people have of teaching in ‘the South’; the protective glass is actually because of COVID). But I always tell them ‘No, no—it isn’t like that.’ I’ve taught hundreds of students at LSU, and I’ve never had an aggressive interaction. Students are generally very respectful and come to learn. They might not always like what I say, they might question what I say (I encourage that), but they haven’t ever been rude or mean about it. Even in the anonymous evaluations at the end of the term, I haven’t had any comments about the science (most evaluations are about how my exams and assignments are too hard). I think the thing that helps me avoid those confrontational situations is me telling the students, ‘Hey look, I won’t ever be telling you what to believe. I know I can’t make you believe something. I can just show you the available data, show you how we build up facts, and then you have to make your own judgment calls on what you accept or don’t. But what I’m teaching, and what I expect you to learn, are the facts scientists have rigorously tested and accept.’

If someone doesn’t believe the moon landings happened, showing them videos of the landings or telling them that you can still see the reflectors and other things the astronauts left behind won’t convince them. I can provide all that ‘proof’, but it is still up to them to believe it. If someone has squarely convinced themselves that it isn’t real, then they have a belief system of mistrust about the people telling them the moon landings really happened. Instead, they trust the anti-science group who tell them it was fake. That’s the core of it: they don’t trust science. For folks like that, you have to start far away from the target subject to get them to understand the fundamental science first. In that way, they can see how (and why) the conclusions were drawn, and hopefully that will help them to trust science in general.

So, who do you trust? Ultimately, we trust ourselves and our network of friends, family and colleagues who have earned our trust. And yes, trust has to be earned. We trust them until we are given a reason not to. As Hemingway said, ‘The best way to find out if you can trust somebody is to trust them.’ I ask you dear reader to trust me, but I also ask you to challenge what I write. If there is information that you don’t trust here, find out more where you can, from the sources I cite and from sources that you find on your own. I only ask that you examine what information you have trusted in the past carefully.

The most important part of understanding a subject is trust. If you don’t trust the source, you won’t believe the information. I can’t make you understand evolution without a bit of trust. How can I make you trust me? I can’t. I can only pledge to you that when I teach evolution, and when I write about the subject in this book, I am doing my best to explain the most accurate scientific information that we have on the subject. I can only give you the most well-tested explanations that scientists like myself have found to explain life on Earth, and I can show you how we got to those explanations.

Facts and Truth

Now that I’ve earned your trust—or at least your willingness to read on a bit—let me tell you that frankly, I don’t know the ‘truth’. Or at least I can’t say with absolute certainty that something is true (‘???!!!’ I hear you think scream). I won’t be lying to you, but I will admit when there is uncertainty involved. Honestly, should you trust anyone that says with absolute certainty they know what is really ‘true’? Of course, acknowledging the inherent uncertainty of knowledge doesn’t stop us scientists from pursuing the truth: we know the truth is out there.

So how do you find out what is true? Well, you can prove that it isn’t false. As a scientist, I test hypotheses (which are answers to questions), trying to prove them false. Can you call what is not-false, ‘true’—maybe? As long as you know that some things are just ‘not false yet’, or ‘not false in this situation’. Some things are so rigorously tested that we don’t question them anymore. We call these facts. Facts are time-tested observations and explanations of how the world works: e.g., an apple drops to the ground when it falls from a tree because of the force of gravity. Via testing and continued questioning we accumulate more and more positive evidence to support a hypothesis. That’s why scientists don’t question biological evolution: evolution happened, and the evidence is all around us. Evolution is a fact. You can’t disprove evolution—there is too much evidence that life gives rise to other life and is modified by time and the environment.

We live in an age where everyone thinks they can get their own ‘facts’ through a Google search on their phone. Most people believe whatever they want to believe. They see a social media post that says vaccines kill thousands of people every year and they share it, and their friends share it. They get the sense that it is well-researched because they see the same article several times, and it makes sense to them within their circle of like-minded friends.¹ It feels like the truth to them, because it seems like everyone else is blind and stupid and not paying attention. But you shouldn’t get your facts from social media alone. There we often only find the watered-down, quickly digestible versions of facts (if not something that is outright false with the intent to mislead or misdirect) because it is becoming harder for the average person to find the actual primary sources of facts—where the information actually was derived and reported. Facts are the results of tested hypotheses. They can be found originally from the primary peer-reviewed scientific literature. One easy way is to use Google Scholar instead of Google (go to scholar.google.com—it’s still Google, just refined and focused on science journal articles), and find papers with a ‘Methods’ and ‘Results’ section (that means the authors tested something and got an answer). Peer-reviewed articles also include reviews and comment pieces that may come up with a new idea. But if you are looking for how someone figured out that Greenland sharks can live over 400 years² or that the oldest fossils are 3.5 billion (3,500,000,000) years old³ or that E=mc²,⁴ then you need to look at the original papers (the primary sources) that discovered and described those facts.* These papers are not easy to read—even scientists often have difficulty reading each other’s papers. But you don’t need to understand every word; you need to get the gist of what the results are, what it means and why it matters. Much of that can be in the abstract, introduction and discussion. You may be surprised how much you enjoy the detective work of finding the source of facts.

In this book, I try to reference the primary literature for every fact so that you can find the original research yourself and see how they came to be. The purpose of this book is to wrap some facts about evolution in a neat package to make them a little more digestible and present them with some background and history.

Some people only believe what they can see, so all of history before their birth is lost to them, and they are blind to all that is beyond their field of vision. Some people claim to not wash their hands ‘because they don’t believe in germs, because they don’t exist if they can’t see them’,⁵ or feel obligated to build a home-made rocket to see if there really is any curvature to the Earth, which they believe to be flat.⁶ Well, good for them. Basically, they are sceptics, just like all scientists. The difference is they don’t trust the people who have microscopes and beakers and who found the microbes that make you sick or that could demonstrably show that the Earth is round (with people even flying all ‘around’ it right now). Some people need to find their own truth and don’t trust anything they can’t see or touch—no scientists or doctors are going to tell them what to do. I don’t think you, dear reader, would be here if you were as lost as them. I hope you are willing to at least learn how evolutionary biologists have come to their explanations. Yes, you will have to trust me a bit, but we can start slow. Let’s get into some history and see how some of those facts about evolution were discovered.

PART II

The Evolution Revolution

Introduction to Evolution

Look at your hand.

Why do you have five fingers?

Why not ten, or twenty or one? Why do so many animals have five fingers? Five seems to be the perfect number for most. Oddly, the first vertebrates to come on to land had many more—seven or eight.¹ These earliest land vertebrates were fish crawling out to land, at first just briefly, then steadily, progressively, for longer periods of time. As the descendants of that lineage became permanently established on land, the number of fingers reduced and stayed that way.²

How about hair? Ever wonder why it is where it is on your body? Or why you have it at all? Well, last I checked we were mammals: see that belly button, love of dairy—yep, you are a mammal. But we are different from other mammals. Why do we stand upright?

Sure, a kangaroo is a mammal that stands upright, but it has a nice thick tail to balance on, and we don’t. ‘What about the ostrich?’ you say. They have beautifully and efficiently fused bones, like their tarsometatarsus, between ankle and feet for strength and stability, while we putz around with thirty-three joints just in our feet.3,4 What are we doing?!? Bipedalism doesn’t seem to have been the best idea. Doesn’t your back, neck and feet hurt after standing a while? Why are our backs curved worse than a busted fender on a rally car, instead of being straight like a rod? And why do we have to balance this giant head on top of that curvy spine—seems like a bad idea. Being warm-blooded is cool when it is cool, but it makes us need to eat all the time. I bet you are hungry now, unlike that cold-blooded python chilling for months without having to snack. And nipples on men—what’s up with that? Evolution, that’s what’s up. Thanks . . . I guess.

But that’s the thing about evolution: you don’t get to start from scratch each time, redesigning the body for each new model (i.e., species). You must build on what came before. And so sometimes you have to take a nice straight loosely connected fish spine and stick it together and prop it up with a few extra twists and turns.⁵

Every time I look at the human body, especially my own (and especially when sitting nearly naked waiting in the doctor’s office), I think of the ways I would fix it. I think of our aquatic ancestors, the animals that first developed a vertebral column (i.e., your ‘spine’), lungs, fingers, big, compartmentalized brains and hearts etc. I think of how much more comfortable we would be in the water, not fighting against gravity, just floating like a happy little astronaut in space. So many of our body parts were first evolved for use in water. I think of the gill structures we had, that you can still see in a developing human fetus, that transform into your larynx, jaws and into the little bones that allow you to hear.⁶ I think of the muscles that help lift the gills in a shark being the same ones that are the muscles of your neck and upper back.⁷

We didn’t get our muscles from sharks, neither did we evolve from them, but we do share a common aquatic ancestor a long, long time ago before bony and cartilaginous animals diverged. We had a more recent ancestor that was a bony fish, making all of its descendants, like us, technically bony fishes too. All of us bony fishes—trout, seahorses, donkeys and humans—are more closely related to each other than any of us are to sharks. Cartilaginous fishes and bony fishes have been evolving independently for a long time (although newly discovered fossil evidence suggests cartilaginous fishes may just be bony fishes that lost bone⁸,⁹), but cartilaginous fishes remained relatively stable in their body types (mostly ‘shark-like’ or flattened, as in the skates and rays) than the bony fish lineage. Some members of that bony fish lineage stayed in the water and continue to evolve to this day (as part of the over 35,000 species of bony fishes living); others left the water and gave rise to all of the land vertebrates or ‘tetrapods’ (Figure 3).

Figure 3: The ‘Vertebrate Tree of Life’ is the same as the ‘Fish Tree of Life’ (since you can call all vertebrates, ‘fish’—because of our shared ancestry); tetrapods in the dashed area (represented by a hen, but you belong in there too—along with other mammals, birds, reptiles and amphibians) as part of the bony fish lineage; specifically you are a lobe-finned fish (of which lungfishes and coelacanths also belong). Things we typically call ‘fish’ are everything else in this tree (with gills and fins), and the dashed portion of the tree is just the group mainly found on land (and who have modified gills and fins as you do).

I sometimes wonder how cool it would have been if cartilaginous fishes had invaded land too. Just think about it—land sharks! But perhaps their cartilaginous skeleton isn’t strong enough to withstand the force of gravity for long (imagine standing on your floppy cartilaginous ear), even though sharks do have more than twice as much muscle as we do (≈75% versus ≈30%).¹⁰ If our aquatic ancestors didn’t have strong bony skeletons (and other organ and sensory systems adapted to survive in shallow waters), they wouldn’t have been able to invade land, and we wouldn’t be here. Sometimes people refer to organisms, especially humans, as ‘perfectly designed’, but our aquatic ancestors had to twist and stretch and rework what they already had. You can’t get to the perfect solution for being a land animal from that fishy starting point (as anyone who has ever had a backache or had food stuck down their throat can confirm).

We share a common ancestor with all life on Earth, but we share common ancestors with some parts of the Tree of Life much more recently than the 400+ million-year-old fish that first came to land. For instance, the common ancestor between us and our closest living relatives, the chimpanzees, was only about 6–8 million (6,000,000–8,000,000) years ago¹¹ (Figure 4). But chimps are our living relatives; there were other, more closely related species that lived even more recently but that went extinct, some even less than 50,000 years ago.¹² So what if there were more human species around today—Neanderthals, Australopithecus and Homo habilis? How would their presence shape our view of humanity? I would like to think that it would open our eyes to our shared similarities and help us fill the gap between humans and other animals. But in reality, I’m guessing we would focus on the differences. Let’s face it—if there were more human species walking around today, there would sadly just be many more flavours of discrimination.

Figure 4: Relationships of living and extinct human species: chimps are our closest living relatives, but there were other species that were much closer to us in the past.

Our species isn’t exactly known for its tolerance, and maybe that’s part of why so many people reject evolution—it puts us too close to the animals, it makes us an ape. Incidentally, all the other living apes besides us—chimps, gorillas, orangutans and gibbons—are endangered because of us (through hunting and habitat destruction). Maybe that same intolerance is why those other now extinct human species disappeared about the same time Homo sapiens showed up.¹³ But who knows, if we blurred the line between us and the rest of the animal kingdom, maybe we would see ourselves for what we are—just another recently evolved branch of the Tree of Life.

As an evolutionary biologist, I like to explain as much as I can through the gaze of history and ancestor-descendant relationships. As the saying goes, ‘Nothing in biology makes sense except in the light of evolution.’ A phrase that evolutionary biologists have heard so often that I can picture their eyes rolling out of their heads and on to the floor as they read this, so hackneyed has it become. (Whatever—established evolutionary biologists are just reading this book to look for mistakes.) No matter how cliched the great geneticist Theodosius Dobzhansky’s words have become, they still ring true. You just can’t explain life on Earth without seeing the connections between organisms, connections we represent as the Tree of Life (Figures 5A and 5B). One organism giving rise to another, passing along traits like those five fingers. Sometimes those five fingers become a bat’s wing, sometimes a walrus’s flipper, sometimes a woman’s hand. The origins are the same, evidence of our common ancestry. But evolution is also the things that don’t make sense: that bad back, our strange knee joint, those man nipples. You’ve got to take the good with the bad, and you can only explain it through the change from one organism to another. Evolution doesn’t make things perfect; it doesn’t do anything to direct any individual or group towards some goal. If you are fit and lucky enough to survive long enough to pass on your genes, then you are a direct part of the evolutionary process. Evolution is not kind; it can be quite cruel (Darwin may have lost his faith thinking about the requirement of so much competition and death related to natural selection¹⁴), but it is not directed: it works without intent or vision towards the future.

Figures 5A and 5B: Two depictions of the Tree of Life. (A) phylogeny with molecular evidence from Hug et al. 2016¹⁵; (B) simplified version showing major divisions.

Incidentally, not reproducing doesn’t mean you are not involved in the evolutionary process. Non-reproductive members of a population are indirectly involved in evolution but aid it by helping others survive, e.g., the doting cousin with no children of their own, the worker bees, etc. They are helping to pass along the genes that they share with individuals who are reproducing.

The product of the process of evolution are the survivors we see living today, modified bits and pieces that we can trace back from one ancestor to another. The evidence is in the genetic code (DNA and RNA) we all share, in the flesh and bones and behaviour we can see and in fossils spanning nearly four billion years of change.

The Great Chain of Being/Ladder of Life

Let’s begin, as so many things do, with Aristotle. His view of life was a hierarchy called ‘The Ladder of Life’ (or Scala Naturae). He set inanimate life at the bottom and humans at the top (angels and gods and such would be added later by others as it transformed into ‘The Great Chain of Being’) (Figure 6).¹–² Aristotle’s work was the most important influence on the West’s understanding of the natural world for more than 1,000 years, and the Ladder of Life/Great Chain of Being metaphor is still how many people understand evolution, i.e., as a linear process with bacteria and plants at the bottom as ‘primitive’ and a straight line from fish → amphibians → reptiles → mammals and then humans as a distinct category at the top.

The problem with that antiquated, single-file view of how life is organized is that it makes you think of life as evolving in a straight line. Even people who accept evolution can get things wrong by taking this linear view. They see all other life besides us as subordinate precursors leading to humans. They see chimpanzees as a step before humans, as if we evolved directly from them. With that view, they see chimps and other apes as ‘primitive’ antecedents of humans, which they are not. They also see a fish as a step before a frog, and a frog as a step before an alligator or some other reptile. Linear thinking can result in a very poor understanding of evolution as well as a distorted sense of ourselves, especially when we push it to include socially constructed views of human races and genders.

Figure 6: Representation of the Scala Naturae, with man at the top of the hierarchy and lesser forms below.

In the bestselling, overtly macho self-help book 12 Rules for Life,³ Jordan B. Peterson argues in Rule 1 that you should ‘Stand up straight with your shoulders back’, building his argument based on the erroneous idea that we are descended from crustaceans and should somehow maintain certain shared innate behaviours with them. Peterson explains how lobsters who are the victors of battles have upright postures: only losers slouch. Okay, I suppose slouching is bad, but we are not lobsters, and neither did we evolve from them. We do share a common ancestor with them, as we do with all life on Earth, and that ancestor gave us some common hormones like serotonin (which we have in common with all other animals). We did not receive those traits from some lobster ancestor, as is implied by Peterson’s writing.⁴ And why cherry pick behaviours anyway? He doesn’t describe how some species of lobsters form hilarious ‘Conga lines’, marching in long single-file migrations.⁵ Apparently, that part of their behaviour isn’t something that he thought was relevant to the modern-male human condition.

In the same book, Peterson argues that human sexuality and gender are essentially fixed because sex and distinct sexes were invented millions of years ago, and that the mother/father/children relationship is the oldest in history.³ But, if you look closer in our evolutionary history or throughout the Tree of Life, there are all-female species (like Amazon mollies, Poecilia formosa), there are multisex/intersex/no-sex species (as in many fungi that have ‘mating types’ or slime moulds that have hundreds of ‘sexes’), there are species that change sex (many fish species) and there are species that reproduce without needing to find a mate in every phylum. You could certainly argue for a variety of sexualities being old.⁶,⁷ The misguided linear view of life led to people thinking that white men are at the top of the evolutionary ladder, a convenient argument to enslave ‘lesser’ beings or to keep the women folk at home barefoot and pregnant. It was that kind of thinking that kept Dalits low and Brahmins high. It is insidious to think these things and imperative we do not use a false notion of evolution to persuade people that they are better than other forms of life because of a false hierarchy. In its worst form, this kind of thinking is extrapolated to all of humanity and leads to racism, classism, sexism, transphobia, homophobia and the like.⁸ To be fair, many more accurate Tree of Life illustrations by well-meaning people still use an image of a random old white dude to represent all of humanity on the branch that represents humans, even though a child, Bruce Lee or Kamala Harris could easily have been picked to represent ‘man’. It is a problem of representation that needs to be corrected. Nothing against old white men, but representation matters; seeing the same subgroup represented as the ideal human on nearly evolutionary tree is damaging.

Let us go back to Aristotle’s hierarchy. Most people today don’t think of humans as having evolved from plants or fungi, so those who conceptualize evolution see that there was at least some distinct branching off from different forms of life. We often visualize life as a branching tree, as in the ‘Tree of Life’, but there are other ways as well (Figure 7A). Many people revert to the incorrect linear view because it is easy to organize life with us at the end and everything else behind us (Figure 7B #1). It would be much more accurate if we visualized life as a bush or bursting firecracker, expanding from a centre. The life around us today is part of a process that started billions of years ago, with everything alive today nearly equidistant from a centre point. Think of the origin of life as ‘the Big Birth’ like the Big Bang that formed our universe, except with life radiating out from that centre (first life), and us and every other living thing as existing on the outer edge (Figure 7B). You are just a star at the edge of the universe, so is your cat, the bacteria in your gut and the giant tube worms living near deep-sea hydrothermal vents. The fossil forms from millions and billions of years ago are closer to that centre; they are long extinct, as are many other forms from the past that have left no trace. Just like the fading firework in the sky, when the centre has burst and faded into darkness, all that remains are the flaming edges expanding outwards: that’s the life we see alive, just a little snapshot of history (Figure 7B #4).

Figure 7A: Evolution is the process that connects all life. The connections between life on Earth are often depicted as a tree-like form (as in Figure 5). But you can also imagine it as more of a web showing an unbreaking sprawling series of interconnected ancestor-to-descendant relationships (as in the top figure)¹. Importantly, extinction isn’t depicted here (but see Figure 7B). Starting from the first life, represented by a single cell (with the white egg-shaped centre) expanding into more, new types of unicellular life represented by the other circles (with no holes in the center), each a different species (steps #10 to #9). That unicellular life keeps evolving, but multicellularity also (step 8) with fungi, plants and animals gaining that trait in their respective parts of the web (multicellularity would evolve multiple times independently). If we focus on just the animal part of the web, we get a diversification of vertebrate life represented by fishes (step #7), and if we follow the vertebrate line you can see that fishes continue to evolve and diversify, but that one fish lineage expands and gives rise to the line that results in mammals including us humans (step #6’). However, as we evolved, so did the rest of life (full step 6), with more unicellular forms too, all diversifying and evolving into the complete web of life (step 6). We tend to just focus on our line of descent (as in the new portion of #6’), but the entire history is much more complex.

Figure 7B: What is missing from Figure 7A is extinction. Step #5 here shows that the earliest life forms gave rise to other life but went extinct along the way (the hole in the doughnut). There may be some fossil remains or other elements, but the centre of this web of life is very old and has left hardly a trace except the descendants, depicted as the younger outer ring, and a few fossil remains (the individual species inside the ring). The scattered life around us today (#2) is just a fraction of all the life that has existed on Earth. Throughout human history, we tend to line up that life with what we see as the most advanced, namely ourselves, as the end of the line, with those we see as more ‘primitive’ forms following behind (#1): that evolutionary line we picture is nothing but an artificial construct, and maybe it is all Aristotle’s fault for getting us to think that way in the first place (see Figure 6).

Box 1: What is evolution?

Evolution is the grand process that led to the uninterrupted chains of ancestor-to-descendant relationships that connect all past and present life on Earth. Evolution is the changing of heritable features like teeth, mating dances or DNA, and those changes leading to new links on the chains (i.e., new types of life). Evolution is the idea of common descent from a single origin and the history of change that explains life on Earth. Evolution is all that wrapped up as a single big explanation or a hypothesis; it is also a theory and a fact. It is a theory nested within other theories and facts. How we frame it doesn’t matter that much, but we often hear evolution dismissed as ‘just a theory’. Let’s dive into why it can’t be so easily tossed aside.

Theories of Evolution

I think about evolution all the time. Whether looking at my hand and wondering about my five instead of twelve fingers, or how my eyes evolved to see that hand and beyond or when looking at my twins and thinking about their identical genomes. Or weeding the garden and getting a prick from a rose bush or the sticky sap from some persistent weedy vines I thought I got rid of last week. I think about evolution when I mow my lawn: ‘Why do you grow back every week?’ I snarl at my grass. ‘You know I’m just going to cut you again.’

If our lawns did stop growing, we would have to explain that strange but natural phenomenon in scientific terms. Perhaps we could see if it only stopped growing if you used a certain type of mower, or because mowing the lawn changes the chemistry of the soil thus preventing growth, or because the grass was somehow ‘learning’ or sentient. Some of those hypotheses are more plausible than others, some easier to test than others. Hypotheses are just possible answers that can explain such phenomena. A theory is the fundamental background information that you need to package hypotheses.

A theory, in scientific terms, is usually an overarching concept that has stood the test of time. A theory for scientists can often be used interchangeably with ‘law’ (e.g., the theory of gravity) but in everyday parlance, ‘theory’ is something that is questionable or that remains to be proven. But even under that usage evolution is not a theory.

There isn’t a single theory of evolution—there are many theories. And more than one of those theories are correct at the same time. One of those theories is natural selection, made famous by Charles Darwin in his 1859 book On the Origin of Species,¹ which sparked ‘perhaps the greatest intellectual revolution experienced by mankind’.*² Another is the theory of evolution by sexual selection, introduced by Darwin in the same book, and which he expanded on in The Descent of Man, and Selection in Relation to Sex³ (a book with a sexier and more interesting title than its contents; sorry Chuck—they can’t all be winners). There is also the ‘neutral theory of molecular evolution’ introduced by Motoo Kimura.⁴ These three ideas are all correct and complement each other rather than contradict.

There are other theories of evolution too that we either have done away with (because they don’t fit empirical evidence) or that are favoured in special circumstances (e.g., those that only apply to asexual organisms). People tend to equate ‘the theory of evolution’ with just ‘the theory of evolution by natural selection from Charles Darwin’, but that’s only one of the theories and just one component of how evolution works. Darwin’s version of evolution is sometimes called ‘Darwinism’, and many of the attacks on evolution focus on that nearly 200-year-old explanation, ignoring all that has come since.

So what’s the big deal about Darwin’s natural selection theory? Well, it is simple and intuitive, and it works. If natural selection was written as a motion by Mother Nature in a parliamentary meeting, it would be: ‘Whereas there is a great deal of variation among offspring, and whereas there is a lot of competition for resources, therefore be it resolved that only those organisms that are best able to survive in an environment may live on to reproduce’ (Figure 8). A shorthand could be: ‘Adults make babies, only some of the babies survive the forces of nature to adulthood to make more babies; rinse and repeat.’ Or perhaps better still, we can explain natural selection as ‘survival of the fittest’. Fun Fact: Darwin used ‘survival of the fittest’ as a short explanation for natural selection only after another biologist (Herbert Spencer) coined the phrase; Darwin used the phrase in the fifth edition of Origin of Species when it became associated with him.⁵

‘Fittest’, as we modern evolutionary biologists use it, is related to reproductive ‘fitness’ or success, not how physically strong you are. Many have misinterpreted natural selection as ‘survival of the strongest’ to terrible consequences for how we treat each other and other life on Earth. ‘Survival of the strongest’ is a popular theme of the eugenics/racial supremacy/Nazi movements that unfortunately are sometimes incorrectly associated with Darwin as ‘Social Darwinism’.⁶ That notion is neither Darwinian in origin nor relevant to how evolution works. (Unfortunately, Darwin’s cousin Sir Francis Galton was a eugenics leader, as was Herbert Spencer, and those associations are partly why Darwin is linked with these awful projections of his ideas even though he never made the same arguments: but he shouldn’t be completely absolved either.⁷)

Natural selection alone can’t explain all of evolution; even Darwin recognized that. That is why he came up with another explanation for the peacock’s beautiful tail feathers and the bright coloration of some animals that obviously make them more conspicuous to predators (hindering their survival). Hence the additional evolutionary theory of ‘sexual selection’—which explains that you sometimes take on traits that might make you less likely to survive via natural selection because those same traits make you more attractive to the opposite sex and more likely to reproduce. You can see why sexual selection is sometimes seen as belonging under the umbrella of natural selection (and sometimes not).⁸ If you need to distinguish between them, think of sexual selection dealing with the competition for mates while natural selection is all about survival. All these fit under Darwin’s brief, but apt, definition of evolution as ‘descent with modification’.¹

Figure 8: Natural Selection—Step 1: Make babies; Step 2: Babies struggle to survive because resources are limited, some die off; Step 3: Babies that prove to be best fit by surviving into adulthood make more babies.

In this case the fish with spots are best fit and grow up to make more spotted fish. Note that all the variation is not lost, a change in the environment may favour fish with stripes next season. [See colour version in insert]

We needed yet other theories of evolution to explain why organisms vary (i.e., why is there genetic variation; why do you look different than your siblings even though you have the same parents; why do identical twins behave differently despite being clones with the same DNA), and for some of those theories we needed to understand genetics—something Darwin and other early proponents of natural selection did not have the means to understand. We also needed more theories, hypotheses, and conjectures to explain the many nuances of life and variation (including non-genetic environmental influences on development). I’ll get into some of that nuance soon, but the point is that when someone says ‘evolution is just a theory’, I say, ‘Nope, it’s a bunch of well-supported theories. Evolution is a fact. Descent with modification is a fact.’ We can’t explain the world and the diversity of organisms without evolution. We can’t prove evolution false with what we observe in the natural world.

One of the best lines of evidence for evolution is that we all share the building blocks of life, DNA. We can use DNA to build the Tree of Life and show the connections between every organism on Earth, including ourselves. Just because we are the only organism that can put together the Tree of Life doesn’t mean we stand apart from it. We are still a piece of the Tree, and as on a map, we can use it to see where we are and where we came from.

In the end let’s remember that natural selection was not the first theory of evolution, not the only theory, and not the last theory of evolution; so let’s throw that hackneyed and false argument out. Despite the existence of other theories of evolution, natural selection is an important insight into the mechanisms of how life evolves, perhaps the most important insight. In many ways that theory evolved in a similar fashion to the mechanism it tries to explain, it survived over competing theories and continues to be shaped over time. Let’s look more closely at its origins.

From So Simple a Beginning

Illustrated by Ethan Kocak

There isn’t a good movie about Charles Darwin’s life, which is a shame, so I asked famed illustrator Ethan Kocak to sketch out a plot for a Darwin movie I wrote. The title was Ethan’s idea, and it, along with the last line, are based on quotes from Origin of Species.

Scene 1: We see a distraught Captain Pringle Stokes, first captain of the HMS Beagle, taking the ship on its maiden voyage off of Tierra del Fuego and taking his own life.

Scene 2 and 3 (top): Young Mr. Darwin, avid collector of beetles, spies another beetle while holding one in each hand. When he pops one into his mouth for safe keeping, it releases an irritant that causes his mouth to foam. He loses all three specimens. Back home, his father is upset with his aimless son (that’s a real quote from dad). Darwin doesn’t want to be a dull physician like his father, but more like his grandfather Erasmus, who was a philosopher of nature (as well as a doctor).

Scene 4: Darwin leaves home on the HMS Beagle on what was supposed to be a two-year voyage but that actually lasted five! He was often seasick, but when they did land on their southern hemisphere circumnavigation (focusing on South America), he uncovered fossils of beasts small and large, witnessed earthquakes and discovered new species; he had a complex relationship with Captain FitzRoy, who was in search of evidence of biblical events. What Darwin was finding instead was evidence of a much older planet than what FitzRoy thought the Bible suggested. Ironically it was FitzRoy who gave Darwin a copy of Lyell’s Principles of Geology, which was one of the first texts to argue for a very old Earth.

Scene 5: Darwin returns to England and becomes a famed naturalist. He enters high scientific society, and his specimens are being analysed by mentors like ornithologist John Gould, who chastised him for his poor field cataloguing of the Galapagos finches. But Darwin intuits that these finches (and other Galapagos animals) had diversified on these islands from South American ancestors. These thoughts lead him to thinking about evolution, and he begins writing the seeds of what will become the Origin of Species. In 1839, he publishes the first version of Voyage of the Beagle and marries his cousin, Emma Wedgewood, who is deeply religious.

Scene 6: He works diligently at home on barnacles, plants, birds, etc.—he has ten children, but several of them die, and he worries if their deaths are due to his consanguineous marriage. At his lowest point, he gets a letter from another naturalist, Alfred Russel Wallace, who is doing fieldwork in Malaya. The letter includes a draft manuscript that is very similar to the ideas that Darwin had been secretly working up for years about natural selection.

Scene 7: After he shares Wallace’s letter with his scientific colleagues, they announce the theory of evolution by natural selection to the world with Darwin and Wallace’s work presented jointly. At this time, Darwin is burying his youngest son Charles, and Wallace is still in the field, completely unaware of all that is going on (he’d be cool with it though).

Scene 8 (previous page): Darwin finally completes his magnum opus, the On the Origin of Species, and it causes a huge stir, including the great debate between Thomas Henry Huxley and Bishop Samuel ‘Soapy Sam’ Wilberforce.

Scene 9: Darwin’s old travelling companion from the HMS Beagle, Captain FitzRoy, is at the debate muttering about the Bible; he would later follow the same sad path as the first captain of that great ship.

Scene 10: Darwin would die many years later (1882), at the age of seventy-three, largely vindicated—he is DarWIN after all, not DarLOSE (to quote a famous Dana Carvey comedy sketch).

Although we dramatized some events here (hey, it’s a movie) it is largely based on the realities of Darwin’s life as told by several biographies, including his own.¹–⁴

The Selection of Natural Selection

Perhaps the most controversial argument in Origin of Species was not natural selection but that there is a single origin of life on Earth. As Darwin put it: ‘All the organic beings which have ever lived on this Earth have descended from some one primordial form.’¹ That was a huge leap forward in thinking; it was particularly powerful when viewed with natural selection as the causative mechanism to explain how we got the diversity of life from that single origin. Darwin was saying that every organism on Earth was related. At the time many people, including popular scientists like Louis Agassiz, didn’t even think all human races had a single evolutionary origin (Darwin did, and that’s a big deal), and earlier theories of evolution assumed there were many origins of life.²

The first major scientific theory of evolution was from Jean-Baptiste Lamarck (1744–1829), for which the shorthand we often use is the ‘accumulation of acquired traits’.³ (Speaking of acquired traits, due to his various accumulated honorific titles, his full name became Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck.) Lamarck thought that different species had independent origins and they went from simple to complex as they picked up features through life, which they passed on to their offspring. The example everyone uses is a giraffe stretching its neck, which would cause it to grow longer; that individual’s offspring would have longer necks than the parent as a result. We know through many experiments that species don’t pass down traits that they acquire in life. For instance, one scientist cut the tails off generation after generation of lab rats, and each generation had a normal tail when they were born (you would have expected a race of shortened or tailless mice under Lamarck’s theory)⁴. But we know intuitively now that acquired traits aren’t passed down—you don’t have blind children because you lost your eyesight; you don’t pass down your muscular physique because you go to CrossFit every week and Michael Phelps’s kids don’t have webbed feet.

I saw an anti-vaccine social media post once about how a future parent wanted to get the flu and measles so their kids would gain immunity—that’s Lamarckian, and wrong. You don’t pass down your immune response to your kids in this way; otherwise, the flu would have died off with the first generations to get it. The anti-vax version of herd immunity, where we don’t take vaccines and fight things off diseases ‘naturally’, is actually Darwinian, because it requires a lot more death. The anti-vax version of herd immunity would require everyone who can’t fight off these diseases on their own to die (leaving behind those with a natural immunity), and most of us don’t want to live in their dystopian reality. This anti-vax version is very different from the real herd immunity advocated by modern scientists, in which most of us would have vaccine-aided immunity and avoid getting the disease in a deadly form. The scientific version of herd immunity would stop the spread of disease with a lot less death than required by the anti-vaccination folks.⁵

An anonymous book was released in Darwin’s time called Vestiges of the Natural History of Creation.⁶ That entertaining text promoted divine intervention as transforming one form into another (including inanimate objects like rocks and stars). Although he disagreed with that idea, Darwin recognized that Vestiges did lay the groundwork for his theory at least in terms of priming the public for a big idea about ‘evolution’ (a term that did not exist in the modern sense until much later). Scholars in Darwin’s time used the term ‘transmutation’ instead of evolution, although Darwin did use ‘evolved’, and it is literally the last word of Origin of Species.

Darwin would probably have never published or completed his so-called ‘abstract’ on evolution, the Origin of Species, without getting a shocking letter from a fellow biologist, Alfred Russel Wallace. Wallace was in what is now Indonesia, working on his own masterpiece on animal distributions (i.e., biogeography)⁷, when a great insight struck him between bouts of malarial fever dreams.⁸ He hurriedly wrote Darwin a letter and a draft manuscript about his own ideas about how species evolved, and those ideas were nearly the same as Darwin’s. Darwin, who had been thinking, experimenting, amassing evidence and procrastinating on the problem for twenty years, was stunned.⁸ Wallace and Darwin both recognized that species come from other species through a struggle for existence and persistence (see Figure 8). Darwin had understood this for years, but he held back because he wanted more evidence. He wanted a huge encyclopaedic multi-volumed text that he probably would have preferred to have published posthumously. But this was his grand idea, a single origin of all life and the struggle for existence that leads to adapting and evolving species: he couldn’t let the upstart Wallace snatch it from him completely. Darwin’s prominent science friends, Joseph Hooker and Charles Lyell, presented Wallace’s paper along with Darwin’s long-concealed work to the scientific elite and published it (all unbeknownst to Wallace still in Malaya, and with the tacit blessing of Darwin who was burying his toddler Charles at the same time).

The next year, 1859, Darwin published what would be an incomplete, somewhat hastily put together masterpiece On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (you can see why I just use the shorthand Origin of Species). It would be the most consequential and readable non-fiction book ever written in the West* and one that would see six editions. Arguably, despite its flaws, the first edition is the best one because it is the humblest and most straightforward version: Darwin wrote apologetically for not having more data, particularly for the source of variation and the lack of fossil evidence (that would come later). In later editions, he gets a little too deep into the weeds trying to explain the source of variation and the nature of heredity (without any idea of how genes work)** and fighting off nonsense creationist ideas. Unfortunately, he had no resources to understand the source of genetic variation, except that he did (in part), in the work of a humble Austrian monk working around the same time but of whom Darwin would never know.

Mendel and the Maintenance of Variation

While Darwin explained that all of life on Earth was descended from a single ancestral form—and most biologists would quickly come to accept that—many couldn’t get away from the fact that most species should have offspring that are less variable than their parents. So they thought Darwin got evolution right, but perhaps not so with all the mechanics. The going hypothesis at the time was that offspring were a mix of their parents, the result of what is called ‘blending inheritance’.¹ Via blending inheritance, a purple mother and white father would make offspring with a ‘blend’ of those traits, i.e., pink daughters and sons. If blending inheritance took place, that would mean variation was lost each generation (i.e., two different-looking parents would make similar-looking intermediate offspring).² Enter Gregor Mendel, an Austrian monk with a love for science and peas.

In one of science’s great insights, Mendel discovered how variation was maintained over generations.³ He mixed hundreds of pure strains of pea plants with different traits (like purple flowers and white flowers) and noticed that he got all purple flowers in the first generation (hmm, variation is lost, but not blended). More importantly, in the second generation, when he mated all those first-generation purple-flowered plants together, the resulting offspring were about three quarters purple flowered and one-quarter white (hmm, the trait that was lost is back). From this result and additional experiments on other traits, Mendel deduced that the traits must be passed down in pairs, with one dominant (let’s call it big ‘B’ from the female) and one recessive copy (call it little ‘b’ from the male). In the first generation, as the male and female portions combine in the offspring, all the dominant copies of a trait (‘B’) block all the recessive copies (‘b’) from being expressed (big ‘B’ and little ‘b’ are paired up in the offspring as ‘Bb’ and you only see the big ‘B’ trait). But in the second generation when the ‘Bb’ mothers and ‘Bb’ fathers meet up and the traits are split up into big ‘B’ and little ‘b’, the two recessive little ‘b’ traits can appear together (without the dominant copy ‘B’) in a quarter of the offspring (Figure 9), resulting in the reappearance of that recessive phenotypic trait (in this case, white flowers).

Figure 9: Crossing dark-petalled pea flowers yielded ¾ dark flowered plants and a quarter white. Why? Mendel deduced there were pairs of what we now know as genetic alleles that separated during reproduction (the dominant ‘B’ and recessive ‘b’). Whenever big ‘B’ was present a dark flower appeared, and little ‘b’ was just from the ¼ of the time there was no big B in the combined seed. What this experiment did is show us how to separate the genotype from the phenotype to explain the maintenance of variation.

Mendel also noticed that all the traits he was studying (seed colour, plant height, etc.) had the same ratio (¾ dominant, ¼ recessive) in the offspring of the second generation after cross-breeding pure strains, but that those traits were not linked to each other (e.g., green seeds and tall plants didn’t always appear together). He realized that those traits were somehow being mixed and divided as they were passed down from generation to generation (we now call this ‘recombination’). For me, Mendel’s discovery of genetic inheritance patterns—now known as the ‘Law of Segregation’ (each trait is represented by a pair of genes) and the ‘Law of Independent Assortment’ (each trait is sorted independently) is one of the most remarkably perceptive insights in history. I mean, he figured out how chromosomes and genes maintain variation, not with microscopes and DNA sequencers, but by growing peas!*3–6 Peas! Now, not all traits are so easy to tease apart (not everyone has either a big nose or a small nose) because they are ‘continuous’ (they are found in a range, like nose sizes, rather than being ‘discrete’). What Mendel did was help establish that there are genetic controls (in the genotype) to maintaining physical variation (in the phenotype) and that blending inheritance was no longer a fatal flaw for explaining evolution.

How important are the mechanisms for producing and maintaining variation that Mendel revealed? We traded immortality for it. Only sexually reproducing organisms follow these Mendelian laws; asexually reproducing organisms (like many microbes and plants but also some vertebrates) can just clone themselves: copying their DNA in its entirety with each generation. This allows asexually reproducing organisms to pass down all their genes to their clones, but it also makes them vulnerable to changing environmental conditions because they lack the genetic variation to help them adapt to change.⁷ Mendel made sense of sex! Not bad for a monk. Sadly, Mendel would never find out how great an intellectual leap he made for humanity.

If only Darwin had read Mendel’s work, he might have been led to the right path to answering how variation was maintained.1,8 Both Darwin and Mendel would die before anyone noticed the simple but magnificent genetic work of this humble monk. It wasn’t until the turn of the twentieth century that people understood that genetics were the link to solving the mystery of inheritance.⁹ Others would discover that the two copies of each trait Mendel noted were the pair of genes on sister pairs of chromosomes and that independent traits were on different places on the chromosome (or on another set), which is why they segregated separately. It was because of the work of Mendel and others who came after that we learned that there was a dominant strain of a gene and a recessive strain that was often masked. This work showed how that recessive trait could ‘reappear’ after several generations of being lost, as in certain diseases like haemophilia. It also explained why blood types appeared in predictable ‘Mendelian ratios’.⁹ Although Mendel’s discoveries were a start, it would be a little longer before people found the real source of genetic variation in our DNA. And as Mendel himself discovered when working on other organisms, not everything is as simple as a pea plant.**¹⁰

Mutants and Mutations

Maintaining variation is one thing, but what Mendel and Darwin could not know is that you can’t have new variation without mistakes. Mistakes in your DNA code are called mutations, and these are the roots of genetic variation. For many people, the word ‘mutation’ conjures up the image of malformed creatures. To kids, a ‘mutant’ might be a laser-eyed flying superhero, but if you want to really impress kids, tell them that they are mutants too. In fact, we are all mutants: mutations are just natural variation in DNA. They are mistakes that happen in the copying of DNA, which is happening right now, happening all the time as your cells divide. Just as even the best proofreaders at the New Yorker occasionally let a ‘dessert’ pass for ‘desert’, so too does the DNA replication machine sometimes write ‘ACTTG’ as ‘ACTG’. And just like the New Yorker error can turn the meaning of a word from ‘a delicious, sweet meal’ into ‘a barren landscape’, the coding error can turn a normal body into a malformed one. But out of three billion nucleotide base pairs in the sex cells (eggs and sperm) representing a human genome¹ made up of As, Cs, Ts and Gs (short for the molecules adenine, cytosine, thymine, guanine), we only get about 10 to 100 or so copy errors in the child that are not inherited from the parents.² A proofreading rate of about 10–8 (or 0.00000001%) that any magazine editor would be envious of.

DNA is the genetic code that is the blueprint for the proteins that make you and control and run most of what you do. An error in the code usually does . . . absolutely nothing—nada, zilch, zero. In one of the most surprising discoveries in our understanding of mutations and evolution, Mootoo Kimura found that most genetic mutations do nothing to change the survivorship or reproductive abilities of an organism, so that the external phenotype (the products of the DNA code that include how you look) remains unchanged.² Kimura called his idea the ‘neutral theory of molecular evolution’.³ Today we associate his idea with ‘genetic drift’, as one of the ways species diverge (via slow gradual ‘drifting’ non-adaptive change in DNA sequences) and a complement to natural selection.

Not all mutations are so-called ‘point’ mutations, which is a change of one DNA nucleotide to another (e.g., an A to a C). The ‘ACTTG’ → ‘ACTG’ example above is called a ‘deletion’, where a nucleotide ‘T’ is deleted; there are also ‘insertions’, where an extra nucleotide is added. These ‘indels’ (short for ‘insertion/deletions’) can have huge consequences depending on where that mutation happens. An indel can change how a protein code is read, so that the protein can no longer be produced. Not making a certain kind of protein can have terrible consequences for the phenotype.

Despite what you may have learned, evolution is not random.* The mutation examples described above do not appear randomly. Some parts of the genome are more susceptible to change than others—in much of your genome it doesn’t matter what changes happen because they take place in non-coding regions outside of the reading frames of genes; other parts undergo ‘purifying selection’, and any mutations are quickly weeded out. Mutations may happen spontaneously and accidentally as cells divide, but they do not become part of the DNA that is passed down every generation, unless it gets into the sperm or eggs. These spontaneous changes only become part of the evolutionary history of a species when the mutation is spread to a representative number of individuals in a population. How does it spread? As individuals reproduce, they pass along their DNA (including mutations) via genetic drift (if neutral) or natural selection (if adaptive). If conditions are favourable, or if the mutation is beneficial, it can spread very quickly or it can disappear in a snap.

Also, despite what you may have heard, most mutations won’t kill you . . . but you might be wondering about those mutations that do. (Everyone loves a good deadly mutation story.) If a mutation is very bad and leads to death, why does that mutation persist? There can be several reasons. For example, some mutations are expressed later in life, after we already passed them down to the next generation (e.g., Huntington’s disease).⁴ Our mutation load grows with age, as cells stop replicating as efficiently as they did in youth (part of the natural stages of getting old called ‘senescence’), aided by smoking, drinking, eating too many sugary snacks and all the fun stuff that makes life worth living, albeit shorter. But those last examples aren’t evolution, because those changes aren’t inherited. Those mutations happen in your normal body cells (somatic cells) versus those that are passed down in your sperm and eggs (sex cells, or ‘gametes’) to the next generation.

Sometimes a deadly mutation can be passed down by being located on a chromosome near a beneficial or required gene sequence—this is called ‘genetic hitchhiking’. Although Mendel was correct about genes sorting independently, it depends on where they sit on a chromosome: genes that are physically close together on a chromosome are more likely to be inherited together generation to generation.⁵ Think of it like loosely shuffling a deck of cards—if you shuffle only a few times, most of the cards that started next to each other will stay near one another. That shuffling takes place between matching (homologous) chromosome pairs that are then separated. After shuffling, roughly half your DNA (as one of the two sets of chromosomes) is rearranged and set aside for making the sperm or egg. You make a lot of these gametes, and each will hold a unique combination of genes represented by a half set of your chromosomes. This entire process is called ‘recombination’. That process is responsible for making the unique mix of your parents’ DNA that is you (when their egg and sperm came together). Think of them as being two decks of cards (one is mom and one is dad): the decks are each shuffled and half of each deck is taken (think of these as being the egg and sperm) to make a new full deck (Figure 10). When it comes to making babies, no one is ‘playing with a full deck’, but you do need to end up with the right number of A’s, Kings, Queens, etc. Think of most mutation being the many small nicks and marks a deck of cards may collect over time, most of which have no consequences to any game you play. If you lose a card while shuffling, that will be a much bigger problem, but not if it doesn’t end up in the half deck (mom’s egg or dad’s sperm) used to make up the new full deck of cards (you).**

Recombination is responsible for removing mutations (even adaptive ones), as the good mutations sometimes get shuffled out just as easily as the bad ones. In that way, recombination is both a force for creating, and removing, genetic variation (i.e., mutations).

It is important to remember that most genetic mutations do not have major consequences for evolution, but small changes can still cause big differences in the phenotype. For instance, Achondroplastic dwarfism is a change of a single DNA molecule from an A to a G that causes insufficient formation of bone from cartilage.⁶ An example of the near opposite case is Joseph Merrick, also known as ‘The Elephant Man’. He had Proteus syndrome, which results from a mutation in the AKT1 gene that can appear in just one cell before spreading like a cancer and causing an abnormal overgrowth of bones.⁷ Some of these mutations are less significant than others; one of my favourites is that a single change in the DNA coding region for one of your olfactory receptors makes the recipient lose the ability to smell the sulphur-y stench of Asparagusic acid, which gives them the impression that their pee doesn’t smell bad after eating asparagus. But guess what? Their pee does stink, just like everyone else—they just can’t smell it!⁸ There is a similar single nucleotide mutation that causes cilantro to taste like soap to some people.⁹ Lucky for them, their naïveté doesn’t lead to any evolutionary fitness consequences, so despite living in ignorance, these non-asparagus-smelling-pee-people and cilantro-tastes-like-soap people live life pretty much like the rest of us.

Figure 10: An explanation of the ‘deck of cards’ metaphor for recombination. Your parents each have twenty-three pairs of chromosomes (forty-six total). Each egg from your mom and sperm from your dad has half the set (twenty-three total). To make a sperm/egg via meiosis, the parental set is ‘shuffled’ via genetic crossover, where pieces from the different sets are recombined. During this recombination, the deck is split into half, so that only one half of the recombined chromosomes is in each sperm and egg. The egg and sperm come together during reproduction, bringing the total number of chromosomes back to forty-six. As recombination takes place, some mutations will be lost (beneficial or not), but this process also creates the unique combination of features that make you and your siblings different from each other and from your parents (in addition to the unique mutations that you gained in this process). (Please note that the process of meiosis from which sperm and egg are made is far more complicated than summarized here.)

Now, I have a confession: I have a rare, potentially consequential mutation. While trying to make babies, my wife and I ran into fertility problems, as many couples do. A miscarriage of an eight-week-old fetus saddened and concerned us, so we had it tested. It was a triploid: three sets of chromosomes (instead of two)—not good. One extra chromosome can lead to diseases like Down syndrome, but a complete extra set is almost always fatal before birth. To understand why it happened, my wife and I had our own DNA tested. It turns out I have an ‘inversion’ on chromosome #8: part of one arm of that chromosome is on backwards. ‘That’s why I’m like this,’ I deadpan to my students to see if they get it (as far as I know I show no external signs of the inversion). Did that inversion cause our miscarriage? Probably not, but the discovery did lead to additional genetic testing of the fertilized egg that would eventually become my identical twins (more on them later).

Big changes and movements of pieces of chromosomes, like my inversion, were thought to be rare. Then in the 1940s, Dr. Barbara McClintock discovered ‘jumping genes’ (or transposition of genetic fragments) that could lead to phenotypic changes—which led to an entirely new avenue for understanding hereditable change.¹⁰ She helped us understand that these changes in the DNA can have no effects, or huge ones, depending on where they happen or where they go. We would also learn that genetic variation can come not just from within the organism, but also from without.

In the 1960s, Dr. Lynn Margulis popularized the theory that sometimes it is cooperation and not competition between organisms that can lead to major changes in evolution. She described how the incorporation of mitochondria and chloroplasts into other kinds of cells led to a ‘symbiosis’ that formed entirely new types of organisms.¹¹ These new organisms eventually would include what became plants, fungi and animals. By making symbiotic relationships with these energy-producing ‘powerhouses’ of the cells, they were able to outcompete other organisms; therefore, that evolutionary shift still fits a Darwinian paradigm.¹² There might even be genes that jump around the Tree of Life via viruses and lead to convergent phenotypes in different organisms, which is one hypothesis about how different fish, mammals and some other organisms evolved placenta-like organs independently.¹³–¹⁶ Perhaps we will discover that other major organ systems also evolved convergently with the aid of viruses. (I wouldn’t be surprised to learn that eyes, in vertebrates and various distantly related invertebrate lineages, evolved independently this way.)

Surprisingly, more of your genome originated from viruses than is ‘functional’ (i.e., actually codes for proteins). At least 9% of your genome has viral origins, while only about 1.5% is protein coding.¹⁵,¹⁷ Even stranger, most of those functional genes we have can also be found in the genomes of invertebrates, or even plants and fungi (these we got from shared ancestry).¹⁸ I’m sure if Lynn Margulis were around to witness the genomic era, she would want us to revisit what it means to be human, or even an ‘individual’. She argued for a ‘holobiont’-view where a single organism is the individual + its symbionts (like the bacteria you carry in your gut and skin). She even argued that the interactions among symbionts was responsible for the formation of new species via a process she called ‘symbiogenesis’.¹⁹,²⁰ These ideas never really took hold, but read the fascinating book I Contain Multitudes²¹ by Ed Yong for more on that debate, including discussions of the works of great modern symbiosis researchers like Dr. Nancy Moran²²,²³ and Dr. Margaret McFall-Ngai²⁴ (who both provide a nuanced and evidence-based take on symbiosis and evolution).

Our understanding of genetic variation has certainly advanced a great deal from Mendel’s time. What Mendel had the fortune of studying were genes in pea plants that resulted in discrete traits like ‘tall’ versus ‘short’ and ‘purple’ versus ‘white’. But there isn’t usually a single gene for each discrete trait like Mendel found in peas. As shown in the examples above, the genetics of variation is much more complicated than Darwin or Mendel could have ever imagined. But science moves incrementally, much like evolution by natural selection, and also ‘one funeral at a time’.*** Luckily, we have evidence for most of the steps in the evolution of scientific ideas preserved in journal articles and books; that isn’t the case for organic evolution.

Speciation: The Formation of New Species

So if your symbionts don’t force speciation in the host as Lynn Margulis’s ‘symbiogenesis’ suggests, is there still a formula for making a species? Yes: isolation + time. You take a part of a population and separate it from the rest. Over time, the unique gene pool in each of those separated groups will diverge through non-adaptive forces (neutral mutations, genetic drift) and adaptive forces (natural selection) due to the different environments those populations find themselves in. To begin with, a smaller population will likely have less genetic diversity than a larger population, so it will already represent a smaller gene pool that can ‘fix’ (to 100% of individuals having it) or lose (to 0%) certain gene variants faster than the larger population. This process is how the versions of the different traits that Mendel discovered (for example) become either one type or the other over time. With fewer individuals to mix with, you may end up with all purple flowers or all white flowers because of the make-up of the population. In fact, Mendel used artificial selection on a few individuals to make pure strains of pea plants for particular traits before he started crossing them for his experiments. In a real environment, there might not just be differences in the size of populations, but also different predators or micro-climates in areas where independent populations are found, forcing differences in adaptations between the separated groups that may ultimately result in speciation.

Think of a species (ruby-throated hummingbird, death cap mushroom, wolf lichen, whatever). There are usually multiple populations scattered around. Some of those are still interbreeding with each other by migrations or via a few individuals that move between those populations. If one of those populations becomes more isolated—let’s say by a river that changes course and divides one land area into two—interbreeding between those populations will be limited because of the new geographic barrier. Given enough time, the accumulated changes will build up to the point that even if the river changes back to its original position, those two populations might have changed enough that they no longer recognize each other as the same species and mate only within their own groups despite the loss of the barrier (Figure 11). Thus, a new species is born.

Figure 11: A meandering river (I.) has an adjacent population of rodents; the river eventually makes an ox-box lake (II.) the population of mice within the ox-bow lake is cut-off from the rest of the population. It is slightly more humid and cooler on the island, and there are fewer hawk predators but also less food and nesting spots. It is also muddier, leading to natural selection for darker fur to camouflage better. Eventually the river returns to its normal shape (III.) but not before the rodents have accumulated enough physical and genetic changes to be considered distinct species.

Speciation due to the formation of a new geographic barrier is called ‘allopatric speciation’, and that is thought to be the most common mode by which species are formed. There are many other ways to make a species, although the ‘isolation + time’ theme is pretty reliable. However, ‘sympatric speciation’, where there are no geographic barriers and little time, is also possible. (Evolution doesn’t like to be told what to do.) Sympatric speciation may be more common in plants than other groups. In plants, duplicated genomes can arise even among adjacent individuals (polyploidy), and although they may not appear externally different at first, plants with different numbers of chromosomes usually can’t interbreed (the chromosomes can’t align during reproduction)—boom, new species.1,2 Sympatric speciation may have even happened in extinct human species (genus Homo) because of a change in immunochemistry (synthesis of sialic acid) that would have caused a chemical fertility barrier³ and giving new meaning to two mates having ‘bad chemistry’. (Besides, imagine trying to date someone who kept going on and on about how delicious the sialic acid was in the mastodon meat and you couldn’t even taste anything besides the salad.)

But what is the definition of ‘species’, you may ask. Well, the exact definition of species is complicated because there is so much variation of life on Earth (past and present) that we can’t all agree on something that works every time for every thing, from paramaecia to dinosaurs. We likely won’t ever have a single all-purpose answer—a situation most of us scientists find very unsatisfying (unless you are a quantum physicist: check out all those particle-waves, the uncertainty principle and Schrödinger’s cat). Biologists want boundaries like countries have: with clear borders. But instead, species more often are amorphously defined like the edges of deserts or what defines a ‘sandwich’ (e.g., is a hot dog in a bun a sandwich?).

Generally, if two populations can no longer interbreed and make viable offspring, we no longer consider them part of the same species. However, there are many exceptions to that ‘rule’. Seldom do we check if different species of organisms can actually interbreed. One way we do check is by making note of hybrids, although the ability to hybridize doesn’t automatically mean the species aren’t distinct evolutionary lineages. Along with many others, I was flabbergasted to learn in 2020 of the ‘sturddlefish’—an artificially crossbred hybrid of a sturgeon and a paddlefish, two groups separated by nearly 200 million (200,000,000) years of evolution (longer than kangaroos and humans have been separated).⁴,⁵ It just goes to show that hybrids, even viable ones, don’t always help distinguish species or even members of different taxonomic families!

Taxonomists generally use differences in heritable traits (e.g., blue scales versus red scales) combined with molecular evidence that lineages are distinct, to name and describe species. Palaeontologists describe thousands of species a year but must rely on different features in limited and often incomplete fossil samples, and people studying microbes with asexual reproduction rely on a suite of differences they expect to occur between species that might not work for vertebrates.⁶ Despite these differences in approach, biologists generally agree that species are real and are the product of evolution, even if they sometimes disagree about when there is enough accumulated differences to make the cut-off between ‘independent populations’ versus ‘distinct species’ (Figure 12).

One reason the Galapagos islands are considered the birthplace of evolution is because Darwin recognized (with a lot of help from taxonomists and years after he left) that the turtles and birds on those separate islands were all slightly different from each other but all must have had a single origin from mainland South America.⁷ These animals differed because each island was environmentally distinct and had different habitats and occupants that forced adaptations. He even recognized (much later) that some populations differed even within the islands as seasonal drying or cooling made some food more abundant than others, so that the struggle for survival shifted with time as did who was ‘fittest’ (i.e., who was reproductively successful)—hence the famous example of Darwin’s finches.*⁸ These examples are what we call microevolution: the small differences between species that occur in shorter periods of time. These changes accumulate over time leading to bigger differences that we call macroevolution (e.g., evolution of flowering plants and associated insects).

Figure 12: A hypothetical example of speciation. Species ‘A’, like all species, is made of different individuals, and like many species is made up of populations in different areas (left side). If separated by a barrier (such as the pointy triangular mountain range) for a sufficient period, the populations may diverge into distinct species (‘B’ and ‘C’). The difficulty is knowing how much change is needed for speciation. It takes place somewhere along the branches from A → B, and from A → C (bottom right). The changes that accumulate during this separation don’t need to be adaptive—they can be neutral changes to the DNA. Ultimately, there can be enough changes to reduce the likelihood of gene exchange even when the now-different species can mingle again (bottom left). These accumulated changes could also include things like new phenotypic differences and preferences in characters of mates, so that the ‘X’-shaped colour pattern is favoured among members of species C, so they don’t attempt to breed with species B which has spots instead of the ‘X’. Or perhaps enough genetic differences arose between members of B and C that, even if they attempted to mate, they could not produce viable offspring.

On Fossils and the Book of Life

Darwin was criticized, fairly, as he noted himself in the Origin of Species, for lacking much evidence from the fossil record to illustrate the gradual change he expounded (i.e., how do you go from micro- to macroevolution?).¹,² The fossils you would expect if life evolved in small steps, from one to another, were poorly known in Darwin’s time. What was known then (and now) is that the vast majority of species that have ever lived went extinct without leaving any fossil remains.²–⁴

If the history of life on Earth were recorded in a book where each page was a species, most of the pages would be torn out, some would be unreadable and some would be shuffled around. We have a good idea of the larger sections—chapters if you will—representing the major groupings of animals, perhaps at the level of something like ‘phyla’ (Figure 13). But most of what we know from the past is what we can read only from the descendants that walk, swim and crawl among us today. These living descendants—as represented by the last few pages of each chapter’s subsection (the subsections representing the level of ‘classes’ or ‘orders’) of the great Book of Life, which remain in relatively good shape—allow us to build the narrative of the entire book.

Some chapters of the Book of Life are in better shape than others, influencing our view. Very few microorganisms leave any evidence of their existence, although it should be noted that the oldest evidence of life on Earth are from microorganisms from over 3.5 billion (3,500,000,000) years ago (stromatolites left by cyanobacteria, and microbial remnants from hydrothermal vents),⁵,⁶ so we have a rough idea how long ago the book’s narrative started on Earth (we can date our planet with geological evidence to 4.5 billion (4,500,000,000) years ago, so we know life took less than a billion years to appear). Unfortunately, the first chapter of the Book of Life is lost; the first life left no ‘Introduction’ for us to read.

Figure 13: The old tattered ‘Book of Life’. Many pages are missing including the introduction that explain the origins of life. Some pages have been shuffled back in, and it remains largely incomplete. Living species are well represented and they make up the pages at the end of each subsection that reflect the major classes of life on Earth. Although major taxonomic groupings are a bit arbitrary, from largest to smallest they are: kingdom, phylum, class, order, family, genus, species. We humans, Homo sapiens, are the last remaining species in the genus Homo, of which there are nearly a dozen extinct species, such as Homo neanderthalensis, the Neanderthals. The other members of our family include chimpanzees and orangutans, and our primate order includes monkeys and lemurs. At a higher level we are members of the class of mammals—with dolphins, platypuses and wallabies; we can identify with hagfish and sea squirts and all vertebrates that at some stage have a nerve cord, a notochord, pharyngeal gill slits and a post-anal tail that make us members of the phylum Chordata; and finally, we belong in the kingdom Animalia with all the other animals.

Most of the earliest pages of the chapters of the Book of Life are biased towards the kinds of life that lived in environments that allowed fossilization and had hard parts (like bone or shell) to preserve. Most things that live in humid, hot environments on land are consumed either by decomposition or scavengers before they can become fossils. Marine fossils are far more abundant than those from land; to make a good fossil, you usually need to be buried quickly in an anoxic environment. The sea provides far greater opportunities for that quick suffocating death than land.⁷ Despite all the biases in the fossil record, we have found millions of fossils since Darwin’s day. In fact, more fossil species are being described every year than living forms. On an average day, between five and ten fossil species are described.⁸

That wasn’t the case when Darwin was alive; people back then were still arguing over what these strange stone forms represented. What fossils did for many at the time was prove that species had gone extinct. It seems obvious now, but for a long time people thought all the life on Earth is all the life that has ever existed and that extinction was impossible. It became harder to believe this when people like Mary Anning (1799–1847) were pulling out not just small, shelled fossils (Anning is often linked to the ‘She sells seashells by the seashore’ limerick), but huge swimming reptiles and flying monsters like the pterosaurs and ichthyosaurs she was the first to discover.⁹ If there was a giant reptile flying over Victorian Europe, people would have probably noticed. Mary’s beasts convinced a lot of folks that these fossilized creatures lived long ago and no longer existed.

The fact that some of ‘God’s creatures’ went extinct deeply challenged people’s religious views: that needed reconciliation.¹⁰ However, the conclusion that some things went extinct didn’t exactly lead to people accepting evolution. Instead, they came up with an alternative—there were periods of ‘special creation’ where a Creator periodically destroyed and repopulated the Earth—a position sometimes called ‘catastrophism’. And in fact, there have been five major mass extinction events that were catastrophes for much of life on Earth. The issue is that there is no evidence of a wholesale repopulating of the Earth with independent new origins of life as described by special creation; rather, all the evidence points to the planet being repopulated by the survivors of extinction (just as mammals replaced the non-avian dinosaurs after the Cretaceous mass extinction).* The special creation take was the leading view of many of Darwin’s scientific nemeses, including America’s most prominent scientist at the time, Louis Agassiz.¹⁰,¹¹ Agassiz had no small role in hardening many in the US from accepting Darwinian natural selection, and his legacy looms large in the current creationist and eugenics movement.**¹²,¹³

Darwin himself discovered some fossil species while in South America, and these convinced him that not only did species go extinct, but they evolved from one another. He found giant armadillo and sloth fossils in South America that he could identify as being relatives of the living animals he was seeing as much smaller forms in the same areas.¹⁴ He deduced that the environment they lived in must have been very different than what he was witnessing around him.14,15 He saw an evolving Earth and organisms that evolved with it.

Instead of special creation, Darwin was heavily influenced by the idea of ‘uniformitarianism’—the idea that the same geological processes that happen today happened in the past, and these slow and gradual changes build up over time to result in the major changes and structures (mountain ranges, canyons) that we see today.¹⁶ Darwin himself witnessed an earthquake in South America that shifted the land in a way that made it easy for him to see that over long periods of time that small (and even sudden) geological changes can add up to major landscape changes.¹⁷ Darwin’s theory of gradual change by natural selection is essentially the co-opting of a geological idea (i.e., uniformitarianism) for biology. The small microevolutionary changes in populations that he observed (such as tortoises and finches with slightly different adaptations for feeding) would lead, over millions of years, to the macroevolutionary differences he saw represented in fossil forms and across the great variety of life he called ‘the tangled bank’.²

The reason Darwin was apologetic about the lack of fossils in the Origin of Species was that there was an expectation that some true ‘intermediate fossils’—things between a bird and a reptile, between a whale and a land mammal or a fish and a land animal—would be known. He needed these intermediates to prove to the ‘special creation’ believers that life was a continuum of change and not separate periods of creation. The first of these remarkable intermediate fossils came just two years after the first publication of the Origin of Species, although it wouldn’t be fully appreciated as that for some time. This fossil, now the most famous in the world, was of Archaeopteryx, the so called ‘first bird’, which had reptilian features such as teeth and claws, but also feathers. This discovery was a shocking find at the time because feathers were only known from birds, and this creature looked much more like a dinosaur, because it was one, along with being a bird.¹⁸ Unfortunately, another Darwin rival, Richard Owen, purchased the fossil Archaeopteryx and intentionally kept it from being recognized for what it was (a transitional fossil) because of what was likely a professional jealousy. Darwin had a complicated history with Owen, the person who coined the term ‘dinosaur’ and wrote early on about ‘transmutation of species’ but who would later write a scathing ‘anonymous’ review of the Origin of Species.¹ Darwin would retaliate by naming Owen in his ‘Historical Sketch’ that made it into later editions (starting at the 3rd) of Origin of Species²; that sketch listed people who influenced his transmutational theory, something Owen would have hated to be associated with.³ That was quite the sick burn from our old boy Charles.

Today we know of lots of intermediate fossils, including several other individuals of Archaeopteryx, but also lots and lots of other feathered dinosaurs that make it a lot easier to read that fleshed out section of the Book of Life.¹⁸–²¹ As we once thought that section of birds to be independent of those of the dinosaurs and other reptiles, we now see the bird section is actually part of a sub-chapter on theropod dinosaurs, and those birds we see flying about today are just living representatives of those dinosaurs. We also have those intermediates between whales and other mammals, and we can follow over time as a hippo-like mammal transitioned to fully aquatic: we can see the nostrils successively move to the back of the head and become the blowhole and how the limbs became flippers and the tail a fluke.¹⁹ We have species like Tiktaalik—the ‘fishapod’ that shows the transition of one type of fish to all land animals, along with fishes that evolved thicker fin bones for fighting gravity while feeding in shallow water and developed choana to allow them to breathe atmospheric air while feeding (choana are what permit you to breathe through your nose). We even have a series of fossil forms that were even more terrestrial than Tiktaalik based on their increasingly less-fishy anatomy.²⁰ We have fossils that help explain everything from how the turtle got its shell²¹ to how humans got their cruddy bodies.²²

Although we will never have a complete Book of Life with all the pages restored, we have enough of the pages to connect major points of the story. If we had all the pages, we could see the complete view of life with all the branches of everything that has ever lived shown instead of just the incomplete ‘Tree of Life’ we have representing what we do know (go back to Figure 7). The pages in the Book of Life aren’t numbered of course, but DNA analyses of living species help us connect who is related to whom today in a way that gives us the outlines of the chapters and much of the index. We also know the Book of Life isn’t read in a single chronological line from the beginning to the end. Each chapter (perhaps in its own volume) is still evolving and changing, each part may be on independent trajectories: i.e., just because a fish came on to land doesn’t end the fish chapter—they are still evolving and diversifying. Likewise, just because some mammal lineage gave rise to humans doesn’t mean the sections on rodents, bears or even other primates don’t continue to add new pages (species). The ends of each section in the Book are the recent species; the only finished sections are those that went extinct and left no living descendants. Sadly, there are many of those, and some of those endings are even being written today because of our actions.

PART III

Questions and Misconceptions

Who You Calling Primitive?

Do a little navel gazing. You have a navel (call it a belly button if you prefer) because of your mother, who was a placental mammal. You developed in her uterus with the placenta providing oxygen and nutrients to you through the umbilical cord plugged into that belly button. When you were born, the cord was cut and you were left with the useless skin-plug remnants of that outlet, and mom is left with her organs squished, her body bruised and a hungry little monster that always wants her milk and won’t let her sleep.

Consider the kangaroo. This large biped—just like us, except aided by a steading tail—gives birth to a small fetus that comes out half-formed from one of her three vaginas¹ (yep). The little fetus then crawls up on its own into a snuggly pouch with nipples in it; it will stay there until it can strike out on its own. To me that sounds a great deal more comfortable than human births. Our large brains require large heads, and human babies have to be squeezed out in much more precarious circumstances than in the marsupial versions. We need to be born early because of our giant heads (if we waited longer our heads would be too big to fit through the birth canal), which make us pretty needy over our first year of life. Can you think of any other animal babies that can’t even sit up and that can barely keep its food down over the first six months of its life? Every time I hold a new-born baby I think, ‘This could use a little more time in the oven.’

We tend to call marsupials like kangaroos ‘primitive’—they shouldn’t be called that, nor really any organisms around today—they are all survivors and parts of the budding edges (the ‘leaves’ if you will) of the Tree of Life. On the Tree of Life, marsupials are the ‘sister group’ to us placental mammals; sister groups are lineages of the same age that diverged from the same ancestor at the same time, in other words ‘closest relatives’.* That means all us placental mammals share a more recent ancestor with the marsupial lineage than we do with the third major group of mammals, the egg-laying ‘monotremes’, such as the platypuses and echidnas.² But before we go and call platypuses ‘primitive’, think of all the cool things they possess, like that duck bill, which gives it the ability to detect an electric field around its prey. They also have conveniently webbed feet for swimming; unlike most mammals with just two sex chromosomes, they have ten (!); male platypuses even have a venomous spur on their hind limbs, and the females make milk but have no nipples.³ Oh, and in 2020, we learned that they are one of just three known mammals that are biofluorescent (read: they ‘glow-in-the-dark’, or at least they do under ultraviolet light).⁴ If a platypus were looking at you, a soft mushy human burning in the sun, they would think they were the advanced ones. If you want to call some features of an animal ‘primitive’ like the egg laying—because it occurred in our evolutionary ancestors—that would kind of be okay, but you could make the same argument for humans having an appendix or wisdom teeth (you know those late developing teeth that don’t actually fit in our mouths).⁵ In biology we call that kind of trait ‘pleisiomorphic’, others use ‘vestigial’; but we shouldn’t call any life form wholly ‘primitive’. And yes, even some of those single-celled organisms you are thinking about have advanced features we lack, like being able to digest uranium, breakdown crude oil and live through long periods of suspended animation. Or just wait until I explain how the lowly E. coli fights off viruses with their CRISPR-based immune system (they don’t need to stay home because of a coronavirus pandemic).

How about the humble fish? They were the first animals to develop backbones, jaws and the basic body plan of all vertebrates, because they were the first vertebrates. It was in the water that our fishy body plan with big brains in our skulls, nostrils and lungs first evolved.**⁶ Compare our common vertebrate body plan to say an octopus. If we had evolved from octopuses, we would have soft-bodied limbs and multiple brains and hearts dispersed throughout our body. All vertebrates are technically fishes (because all vertebrates share a most recent common ancestor that was a fish). One branch of fishes came onto land 400 million (400,000,000) years ago: these are the sarcopterygians, or lobe-finned fishes, and gave rise to Tiktaalik and other tetrapods (the roughly 40,000 living—and many extinct—species of mammals, reptiles, including birds, and amphibians). Other sarcopterygians were part of lineages that stayed in the water. These include living forms like coelacanths and lungfishes.⁷ Lungfishes have a lung (surprise, surprise) and can drown if you hold them underwater. Coelacanths swim in a doggy paddle and have thick limb bones that have the homologous structures of a radius and ulna that you and all land vertebrates have instead of the thin flexible fins you think of in most fishes.⁸ Coelacanths and lungfishes are more closely related to us (as we are also sarcopterygians) than to any non-sarcopterygian because we have a more recent common ancestor with members of these lobe-finned fishes. Therefore, a coelacanth is also more closely related to you than it is to a trout or a goldfish.

Figure 14: Figures depicted the fishy tree of life (a.k.a. vertebrates) including tetrapods. Note how we are more closely related to coelacanths in the ‘lobe-finned fishes’ lineage of both trees. Reprinted from Braasch et al. 2016.⁹

Going further back, you are also more closely related to a goldfish than to a shark, because you have a bony skeleton (like goldfish and all bony fishes) and not a cartilaginous one (like sharks).⁹ You might consider a shark a fish, and you would be right; but you might also think all fishes swimming around the oceans and rivers are more closely related to each other, but on that point you would be wrong. Cartilaginous fishes like sharks have a more recent common ancestor with each other, and bony fishes are all more closely related to each other than to any other group. Another way to think of it is that cartilaginous fishes have a different chapter in the Book of Life than bony fishes (see Figure 14). The cartilaginous fish chapter has fewer species pages than the bony fish chapter, and the bony fish chapter includes not only tuna and tarpon but all land vertebrates, because again all tetrapods descended from a common fish ancestor. Yep—you are a fish my friend (a ‘fish’ being any vertebrate) . . . a fish out of water, and that’s why your body is a flop.

Our Crappy-Crappie Bodies

Your body is a disaster. I don’t care if you look like Padma Lakshmi or Michael Jordan. We are all hunks of water-logged flesh, hanging off of sticks of collagen and calcium, made up of teeming pockets of bacteria that are held together by strings of blood all covered in an oily skin bag. We are frail naked apes with giant lollypop heads with exposed and vulnerable dangly bits that are so ill-equipped for life that we get tired after standing up still for ten minutes. Why? Again, we are literally fish out of water.

We are taught to think we humans are perfect: no less than the pinnacle of evolution. Hogwash. The only thing we got going for us are our big brains, and we use those brains just enough to think we are better than everything else and to build things to make us feel important but that will also destroy the planet and ultimately ourselves—time for some humility.

Look at your stupid kneecaps. Why don’t we have a ball-and-joint like your shoulder, or at least something simpler than an oddly shaped bony wedge with a network of rubber-band like tendons and ligaments attaching it to the adjacent bones that are all so close together they end up rubbing together in old age?*¹ Why do we walk upright? Ugh. I get tired just thinking about standing. You are probably sitting right now or wondering when you will get to sit or lie down next. That’s because we are constantly fighting gravity. You know who doesn’t have that gravity problem? A fish in water.

Consider the teleost—which means ‘end bone’ or ‘perfect bone’—these advanced bony fishes are the product of 500 million (500,000,000) years of fishy evolution (most living fish species belong to lineages that are very young in evolutionary terms²–⁴). These 20,000 species are the real pinnacle of bony fish evolution (and have nothing to do with the lineage of sarcopterygians that broke off separately 400 milllion (400,000,000) years ago and came onto land and made you).⁵ Most teleosts have a balloon-like swim-bladder that lets them float around leisurely, making them neutrally buoyant in the water. I am thinking of the seahorse at rest lounging around with their tails holding on to a leafy plant in the water, like a jaunty tethered astronaut in space.

Teleosts have neat little spool-shaped vertebrae that are loosely connected to each other in a nearly straight line; this ‘backbone’ is strong enough to propel them through the water with a flick of a tail without having to worry about hurting their backs or twisting a knee. Their heart is up close to their head, and so they can get oxygen quickly through the gills and then pump that blood around the body with the tranquil blood pressure of a relaxing bon vivant. Even if they get injured, they can recover quickly, and some fishes can regenerate injured heart, brain and spinal cord tissue.⁶,⁷

Instead of perfecting the early fish system for the aquatic world as teleosts have, we had to take the early lobe-finned fish system and make it work for life on land; and we’ve suffered the consequences of coming out of the water ever since. We have higher blood pressure to pump against the force of gravity, putting a lot of strain on our weak heart, which has just one coronary artery feeding it blood: if that little drain gets clogged (as many people find out every day when they have a ‘coronary’), you are toast. Odd that the heart, which efficiently circulates the entirety of your blood in about a minute, feeds its own need for blood through just one little artery. Standing upright makes the pressure worse, as we have to fight gravity more as we stand. That is why it is recommended you lie down when you need to take down your heart rate (like after a venomous snake bite or a coronary). Fish hearts are a lot more fool-proof with big pools of blood (as in the large sinus venosus) that don’t get clogged just because they had too many fatty jellyfish sandwiches.

Our odd land-based circulatory system made it not just harder to oxygenate the blood but also led to one of the strangest parts of our anatomy: the laryngeal nerve. That nerve supports the larynx or ‘voice box’, which develops from the pharyngeal arches derived from the gill arches of our fishy ancestor.⁸ The vagus nerve (cranial nerve ten or ‘X’ for those of you dissecting a shark, sheep or human brain in an anatomy lab) connects the brain to the heart and helps determine the heart rate and speed of respiration in fishes (via the sixth pharyngeal arch).⁹ In humans, the larynx descends over the course of our development and is suspended by a hyoid cartilage (which fishes also have for supporting their gills), and this voyage down the neck pushes the laryngeal branch of the vagus nerve down towards the heart and back up the throat in an awkward loop (instead of the direct path between brain and larynx). The fortuitous route would be true of any tetrapod and may have approached 30 m (or roughly 100 ft) in long-necked sauropod dinosaurs!¹⁰ That’s a lotta nerve.

It isn’t all bad. We do have the advantage of getting more oxygen directly from the air than from water (which has a lot less oxygen), but gas exchange is more difficult through lungs than with gills. But we mess that up too by using the same tubing for breathing as for feeding, and we have just a little piece of flappy tissue (the epiglottis) to keep food from going down the wrong pipe. And that never fails—(choke, choke) right.**¹¹ I’d rather have the body of a crappie (the fish) than our crappy bodies.

Fishes also keep their baby-making system snuggly inside their body. Not us. From boys to men, we have our meat and potatoes hanging outside of the body cavity because we produce too much heat inside (which would kill developing sperm). But of course, the testicles have to start off inside the body (because that’s where it was in our ‘cold-blooded’ ancestors) in-utero then migrate out. As they drop, the testes drape over the ureter in a half-knot that causes prostate issues later in life and potentially hernias early in life.¹ TMI Fun Fact: I had an undescended testicle that required an operation as a child—maybe that’s when I started hating the human body.

We can see in our bodies the evolutionary connections we have with more recent ancestors too. We still have the remnants of a tail (which is just an extension of the spine) as the coccyx; and we get goosebumps to raise non-existent fur on our bodies (which we lost in becoming ‘naked’ apes). Yes, we had hairy ancestors with tails, but no, not from monkeys. Unlike a common popular myth, we did not evolve from monkeys. We share a common ancestor with monkeys that led to both tailed monkeys and to the tail-less great apes (of which we are one).

To truly know the answer to ‘Where are we from?’, you need a map. That map is called the ‘Tree of Life’, and we all should learn how to read it to understand where we are in ‘life’.

The Tree of Life

I study the Tree of Life: it is the visual representation of the relationships between the species that have lived on Earth. The tree is a way of visually describing who is related to whom in a series of ancestor-to-descendent relationships (go back to Figure 5).
I focus on the part of the tree related to animals, specifically the part related to vertebrates, and even more specifically, I study fishes. If you zoom in on the fish part of the tree and the roughly 35,000 living species (and the extinct ones we know about), you will see that the fishes only represent a small fraction of life on Earth.¹ There are more than 350,000 described species of beetles alone, more than any other animal group, and almost the same as all of plants and about 10X the number of described bacteria.2,3 Part of the reason for that surprising result is that there are more entomologists describing species than microbial taxonomists. There are surely more bacteria species than beetles, but they are harder to describe. For a beetle, you need to justify the novelty of the new taxon using distinct physical differences—such as the varying shape of the wings or colour patterns; for a microbe, you sometimes have to describe physiology and have molecular evidence since they are invisible to the naked eye.⁴ Perhaps if microbes were the size of insects or basketballs, things would be different. In recent years, we have been able to sample environments and guesstimate the number of new microbial species in an area, but identifying their presence is quite different from identifying, naming and describing those species.

The tree tells us about more than species diversity—it also tells us how organisms are related to each other and which groups are ‘real’. Groups are real (also called a ‘natural group’ or ‘monophyletic’) if they reflect an ancestor and all their descendants, e.g., the ancestors of horses and all horse species that have ever lived or went extinct. The Tree of Life can also tell us how groups are ‘not real’ or ‘not a natural group’. And some of our favourite groups are ‘not natural’: lizards (when you don’t include snakes), or raptors (owls and hawks and other birds of prey that kill with taloned feet) or the Great Apes, if you don’t include humans. It would be like cutting the flowers off an azalea and saying it was just a flowerless shrub, while also saying the flowers were generated independently; you can’t take a branch out of the Tree of Life without recognizing all the little buds, leaves and twigs coming off that branch.

Sadly, even my favourite group, ‘fishes’, aren’t a ‘natural group’. I know, I also felt lied to the first time I realized it, but it’s complicated. Because fishes include cartilaginous species and bony species, fishes are only a natural group if you place the shared common ancestor of both at the root of all vertebrates. So, unless you can call all vertebrates ‘fishes’, it isn’t a natural group. Same thing if you remove the ‘tetrapods’ from fishes. Removing members of a natural group makes it ‘unnatural’ because then it would not include all the descendants of an ancestor and, therefore, wouldn’t reflect the true evolutionary history of a lineage. It would be like not counting your grandmother as part of your family; you might have disowned her, but biologically you are still in the same family. So, unless you admit you are a fish, along with snakes and pandas, salmon and peacocks, you are subscribing to an unnatural grouping, and you are breaking up our family! (Go back to Figure 14.)*⁵

Our understanding of the Tree of Life changes daily as new relationships are hypothesized, as new species are described and as new data becomes available. Most of the tree remains stable, particularly the largest parts near the trunk, as most of the changes are at the tips. The study of the relationships on the Tree of Life is called ‘phylogenetic systematics’ (or just ‘systematics’).

The study of systematics has changed dramatically in my career, as most systematists studying living species now almost exclusively use DNA to determine relationships. As more data becomes available, especially with genome-scale data (‘phylogenomics’), the Tree of Life changes. The tree itself can therefore be seen as a living, evolving thing, almost like a real tree. Check out the ‘Open Tree of Life’ Project that uses the tree and leaf metaphor for the continually updated Tree of Life.⁶

The Tree of Life represents ancestor–descendant relationships, but it does not have any ancestors named on it. All the ‘tips’ on the tree are species, while the ancestors are represented by the nameless ‘nodes’ or bases of the branches. Evolutionary biologists never say, ‘This species is the ancestor of these species’, unless we are talking about dogs being the descendants of wolves or cases of artificial (human-directed) selection that we have witnessed. We don’t look for ancestors, because ancestors are generally ‘unknowable’—it is unlikely that we stumbled upon the individual, population or even species that gave rise to a new lineage. How we could even recognize an ancestor as such is not clearly defined. What we are really looking for are ‘sister lineages’—groups who are each other’s closest relatives, who evolved from a ‘Most Recent Common Ancestor’ (or ‘MRCA’ as the cool kids abbreviate it) together. These sister-group relationships can help us explain how evolution happened in a more precise language. We can say, ‘These sister lineages split off when South America and Africa broke apart, or when this mountain range formed or when one of them had a duplication event in its genome.’

We develop hypotheses of relationships based on modelling the evolution of heritable characters. We look at which features are shared and were modified by a group of organisms: the transition of scales to feathers, for instance, define one group of theropod dinosaur, the group that includes birds. Likewise, the transition from a single DNA base from A to a C might be evidence that a particular group of bacteria are each other’s closest relatives (although we generally have much more evidence than that).

The Tree of Life is a road map of this planet’s evolutionary history; unfortunately, it is incomplete. It is incomplete because we don’t know all the living species, and we certainly don’t know most of the 99% of species that have gone extinct in the nearly four-billion-year history of life on Earth.⁷ The life span of most species is short. The species we see alive and around us today are all about the same age as our species, Homo sapiens; we living species are all just a few million years old or less.⁸ We living species are all about equidistant from the centre, ‘the big birth’ that was the common ancestor of all life that is alive today (go back to Figure 7). Some living species look superficially like some of the earliest life on Earth, and in fact, for about two billion years most of life looked, well, pretty boring—all of them just individual single cells.⁹

But despite their unassuming appearance, there is a huge diversity within that unicellular life. Some life in extreme environments today probably look like the planet’s earliest life—we call them extremophiles and many are members of the ‘Archaea’.¹⁰ They live in near boiling water or hydrothermal vents or other inhospitable (at least to humans) places that may have resembled the Earth around four billion years ago. Other unicellular life incorporated mitochondria and chloroplasts; although these resemble other organelles in our cells, they lived independent lives on their own before they were incorporated.¹¹ Unicellular organisms with nuclei are called ‘Bacteria’; all the ones that are multicellular are ‘Eukaryotes’, and we are in that group.¹² (Yes, of course there are some unicellular Eukaryotes,¹² because evolution, you know, doesn’t like to be bossed around.) But how did all of this life come to be in the first place? Well, we don’t know. Not knowing is okay, it is where we get our power as scientists, in admitting and confronting our ignorance. From doubt and ignorance, we get curiosity, and from curiosity we get observation and experimentation. And hopefully from that we get answers. But even the answers are just hypotheses—we need to raise doubts and test them again and again. And that’s part of why we don’t know how life originated with any firm certainty—yet. (Please hold off until the end of the next section to sigh in exasperation.)

We do know that life gives rise to life. You were always alive, and the sperm and egg cells that combined to make you were alive. And so you are part of a chain of unbroken living forms that goes back to the common ancestor of all living things. There were likely living things before that, but they had less successful descendants that didn’t make it to today. But how do we get that first ‘life’? And what is ‘life’? Defining ‘life’ or ‘living’ is actually pretty hard. Many still use Aristotle’s definition of something that is capable of ‘self-sustenance, growth, and reproduction’,13,14 but some organisms only gain nourishment from what bacteria digest for them (e.g., mouth- and gut-less giant tube worms, Riftia pachyptila)¹⁵, many unicellular organisms don’t grow and not every living thing reproduces (e.g., sterile worker bees). I will alter that definition a bit to include an evolutionary perspective in the next section.

The Origin of Life

There is no knowledge without uncertainty. That statement isn’t very satisfying, but that’s the truth of it. A good scientific moto could be one often attributed to Mark Twain: ‘It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.’

Where did we come from? Other life. Where did the first life form come from? We don’t know for sure. We just don’t know. We don’t know because we don’t have a fossil of the earliest life or of the intermediate between the non-living and the living—the ultimate transition. Not that we haven’t looked. Just as with Archaeopteryx, scientists thought they had discovered an important transitional form shortly after the publication of the Origin of Species. ‘Darwin’s Bulldog’, Thomas Henry Huxley, thought he had discovered a ‘protoplasm’ that was potentially the transition between inanimate and animate life. He named this odd apparently animate goop from the Atlantic sea floor Bathybius haeckelii. Unfortunately, what he thought was an example of a very simple life form turned out to be an artefact of staining and preserving sea water.¹ To his credit, he owned up to the mistake. Ernst Haeckel, ‘Darwin’s Chihuahua’™, and the bacteria’s patronym, took longer to accept the error and perpetuated the myth (he was also wonderful at creating neologisms such as ‘ecology’, ‘phylum’ and ‘First World War’). Few serious claims on discovering the greatest transitional form have been made since.²

We are left with no direct evidence of how inorganic matter transitioned into animated life. I’m sorry—that’s just how science is sometimes. Not knowing things with absolute certainty is especially true in the historical sciences; in these fields we must rely on information from the present to infer the past, because, well, we can’t go back in time to make direct observations.

We also haven’t managed to produce life independently in a laboratory or observe it evolve on another planet. That’s unfortunate, but the lack of direct observations doesn’t mean it didn’t happen here or elsewhere. You may not have met your great-great grandparents or even have pictures of them, but you know you had them and that they were human beings. It’s too easy to wave off the origins of life on Earth as unexplainable, but that isn’t the scientific way.*³ We have to keep asking and looking for answers.

There can be a multitude of ways that you can answer ‘Where did life on Earth come from?’. Your answer or hypothesis could be, ‘God created life on Earth’, and I would not be able to prove you false, because there is no test for ‘God did it’. If you murdered your neighbour and told people, ‘God made me do it’, they couldn’t prove you wrong either, but you would still go to jail. So, let’s stick to observable and testable ideas of nature. There are two alternative hypotheses we can work with for studying the origin of life. Hypothesis 1: RNA/DNA based life on Earth is extraterrestrial in origin, getting here via a meteorite or some other means; a.k.a. the panspermia hypothesis. Hypothesis 2: life evolved on Earth from inanimate matter, a.k.a. the abiogenesis hypothesis. Let’s look at what we can observe in nature to test and support or falsify** these ideas. In the end, both hypotheses might be correct or both could be wrong, and there may be another alternative we haven’t thought up yet.

If you look at all life today, it is DNA based, therefore, the so-called ‘LUCA’ (Last Universal Common Ancestor) was likely DNA based as well.⁴ Did it always have to be? No—earlier life forms may have used the simpler RNA form and maybe an even simpler replicating code before RNA, but all standard-issue ‘life’ today is based on DNA, at least for what is in the Tree of Life. There are also viruses that use RNA for their genetic code (albeit they still need DNA intermediaries), and viruses are still around. Maybe some earlier form of virus that didn’t need DNA is the intermediate group we are looking for. It is possible that the first life on Earth looked something more like an RNA-based virus, but it was perhaps something even simpler, something that left no descendants we can study today. We tend to define life based on the fact that all the living things we know about use DNA. But what if we found viruses on Mars that somehow could replicate on their own? Or methane-eating tardigrades on Saturn’s moon Enceladus? As we discover potentially new life forms elsewhere, we might even discover evidence of them on our own planet and realize we just didn’t know what we were looking for because of our overly narrow definition of life.*** Maybe life was an inevitable outcome of the forces of nature. There are compelling arguments that Jeremy England’s theoretical work is a ‘Physics Theory of Life’.⁵ I’m sure there are other theories out there, and ‘out there’.

For me, ‘life’ should be defined as any organism that can inherit or pass down heritable traits and evolve (by being susceptible to the neutral and selective forces of nature). All living things we know of evolved and carry heritable information via nucleic acids (DNA or RNA)—maybe that is all we need to think about to find the single source of all other life or at least the LUCA. (The Last Universal Common Ancestor doesn’t necessarily need to be the first thing that ever ‘lived’, just the most recent thing that all living forms are descended from.)

Let’s first look more closely at nucleic acids. What does DNA do anyway that is so special? Well, DNA makes amino acids (with help from RNA), which make proteins, and the proteins make you. And they make the things that make you, and they make the things that make you do the things you do. You can think of yourself as essentially a vehicle for DNA replication, i.e., we organisms are just a tool for DNA to make and spread more DNA. Considering all they do, amino acids (those intermediates between DNA and proteins) can be made pretty easily created. In one of the most famous experiments of all time, Stanley Miller and Harold Urey recreated the early Earth’s atmosphere within closed chambers of gas, they then added electricity and—voilà, that created many of the amino acids that we observe today.⁶ So that’s a good case for the abiogenesis hypothesis, except that making proteins from the exact sequences of amino acids is rather complicated and intact amino acids have also been found on meteorites,7,8 a strong case for panspermia. However, the great and incomprehensible vastness of space makes the panspermia hypothesis less likely and just kicks the can of abiogenesis from Earth to someplace else.

Having said that, it is notable that most of the water on Earth is probably extraterrestrial and older than our solar system.⁹ Where there is water, there may be life, and there is water all around our neighbouring planets. There is much more water (as ice or flowing) on three of Jupiter’s moons than on Earth, even sizzling hot Mercury has ice: water is not rare in our solar system, but that doesn’t necessarily mean there is life in those places.¹⁰ News in late 2020 of their being water on our moon and potential biochemical signatures of life on Venus were still a shock and recalibrated this debate.¹¹ The jury is still out on life on Venus, but I give it more credence than those that suggest SARS-CoV-2 has cosmic origins.¹²

Even with those alternative hypotheses, we still have evidence for all life on Earth having a single common ancestor. What other evidence do we have? All life on Earth uses left-handed optical isomers of amino acids instead of right-handed ones (think of them as left or right mirror images).¹³ And all life on Earth also only uses right-handed sugars, so there is that too.¹⁴ Right-handed optical isomers of amino acids and left-handed sugars are also available for synthesis and could easily have been the basis of life, but they are not. That means all organisms on Earth use the same genetic code and machinery for protein synthesis and metabolism. You can’t metabolize right-handed optical amino acids or proteins and left-handed sugars, and neither can an amoeba or a blue jay. (Somebody please make diet food out of right-handed optical isomers and right-handed sugars already! Get me that good ‘anti-chiral’ cereal.)

The fact that amino acids are easily made in the lab or found in space isn’t enough to explain how we get from these ‘building blocks of life’ to actually evolving life. We need something to copy the code that makes those building blocks (like how RNA helps to make these amino acids or like what the enzyme polymerase does to DNA). Notably, scientists replicate DNA in labs across the world by doing PCR (polymerase chain reaction), and we use a polymerase extracted from Thermus aquaticus, an extremophile microbe isolated from a hot spring in Yellowstone National Park.¹⁵ Why does that matter? Because the hot springs are probably one of the closest things today that we have to what our planet was like when life was evolving over three-and-a-half billion years ago, shortly after the formation of the Earth.¹⁶ How do we know life on Earth may have been around that long ago? Fossils, duh. Well . . . kinda.

The earliest fossils of life on Earth are actually not of the earliest known life but of the by-product of what they created, kind of like not having the Ancient Egyptians around but having their pyramids. We have the accretion structures (layered mound stromatolites)¹⁶ formed from layers of ancient blue-green algae (also called cyanobacteria); we can still watch this process today with modern algae. So, although we don’t know exactly when life evolved or how, we know it must have happened by about 3.5 billion (3,500,000,000) years ago, the time we start finding traces of life in the fossil record.

The History of Life

Once we get life, which must have been quite exciting, it gets boring for a while, like a couple billion years a-while. ‘The boring billion’ is called that because we have year after year of just unicellular life evolving,¹ and most people can’t wait to get to dinosaurs—there is a reason there isn’t a movie called Proterozoic Park. But if Life on Earth is a gumbo, you need the roux before the rest. People misunderstand this transition (from just ‘unicellular’ to ‘unicellular + multicellular’) as life getting more complex over time—I don’t; there is still plenty of unicellular life evolving, in fact they still dominate the Earth and they dominate your body.² We wouldn’t last long without these microbes (most of the cells in your body are actually microbes, and most of your genes had microbial origins, so who are you exactly?). There is a good argument that we are just a bus for these tiny ‘simple’ creatures.*³,⁴ In those boring billions, unicellular life was learning how to do essentially everything on their own, so when we came along they were ready to use us as just another substrate to invade. Microbes have collapsed the functions of their own lives so that they are fully in charge of all those processes of life, while much of animal and plant life rely on microbial symbionts to carry out many ‘duties’ (pun intended, read: digestion) on their behalf. In short, microbes can live without us, but we cannot live without them.²

In those first few ‘boring’ billion years of life, lots of stuff is happening. Within that long period of time, microbial life gains the ability to live independently, others work together, some can metabolize hydrogen sulphide and others can photosynthesize (they could eat sunlight, water and carbon dioxide and turn it into sugar and oxygen)—those last ones will change the planet.⁵,⁶ The invention of photosynthesis potentially meant extinction for lots of living things, it is hypothesized that oxygen was perhaps the deadliest thing ever released into the atmosphere. You think we are bad releasing CO₂ and warming the planet. Releasing oxygen as a by-product of photosynthesis was worse, at least a few billion years ago.⁷ Oxygen was a dangerous poison, and it still is. Oxygen paired up (O₂) is great—we need it. But alone, oxygen is a ‘free radical’. That’s why your favourite sports beverage label is always talking about ‘antioxidants’. Free oxygen is a ‘radical’ because it binds to random stuff, like your DNA, and causes mutations.⁸ When microbes started making oxygen, it started slow, but that mutation-causing oxygen did just that—caused mutations and let life evolve harder, better, faster, stronger. After ‘The Great Oxygen Event’ comes the great diversification of eukaryotic life, which were at first just more instances of unicellular life with a separate nucleus with DNA as chromosomes.⁹ Eventually, these eukaryotes would incorporate mitochondrial cells that needed lots of that delicious atmospheric oxygen (O₂ is about 20% of the air now) to make energy. These supercharged eukaryotes would eventually also become multicellular plants, fungi and animals—each independently, and a number of times within each group.¹⁰–¹³

The independent origin of multicellular life is a real mystery. The simpler explanation would be a single origin of that complex trait, but that disagrees with our current understanding of the Tree of Life.¹⁰ Some people point to a global ice age, a ‘Snow-Ball Earth’ period about 650 million (650,000,000) years ago, that may have contributed to the evolution of multicellular life, as if everything had to huddle together and learn to cooperate to survive the cold.¹¹ I often think that much of alien life, which is most certainly out there somewhere among the trillions of planets and stars, will likely be as boring as the Earth was for its first few billions of years. Who knows, maybe aliens will be as cool as E.T. or Chewbacca; it just might be unlikely given our own planet’s history. While we are on the topic of science fiction, I always liked that in H.G. Wells’ The War of the Worlds, it isn’t guns and missiles that defeat invading aliens but microbes, who we have evolved with for ages that take down the sterile uninoculated extraterrestrials.

So maybe microbes aren’t all that dull, but let’s move to what we are more familiar with. About 540 million (540,000,000) years ago, we have an explosion: the ‘Cambrian Explosion’. Multicellular life gets a backbone, and with it we get the first fishes from which all other animals with a backbone spring, all with the same basic body plan.¹⁴ We also get a wild variety of organisms, including some that don’t last very long and that we never see again or that we have a hard time linking to modern forms.¹⁵ Evolution was experimenting with different body types, and the ones we see around us today are the ones that survived from that time.

While microbes keep evolving, so do things in the water; starting about 500 million (500,000,000) years ago, plants, fungi, invertebrates and eventually fishes start to colonize land, and it doesn’t take off (relative to the diversity in the oceans) until much later.¹⁶–¹⁸ (New evidence suggests unicellular fungi got to land first about a billion years ago,¹⁶ and molecular evidence points to an earlier invasion by plants too.¹⁷) From the fishy ancestors we get all the land vertebrates you think of today, we don’t get mammals until about 200 million (200,000,000) years ago, some are as big as the dinosaurs, but most are small, just like today, where most mammals are rats or bats.**¹⁹–²¹ From these rat-sized things, we eventually get the lineage that gives rise to humans. But when I say humans, I don’t just mean our species—until pretty recently there were about a dozen or so species we could call human or at least ‘homininans’ (members of the Hominina: the branch on the Tree of Life that is the sister group to chimpanzees and includes us Homo sapiens and our closest extinct relatives).²²,²³ But that’s just our part of the Tree of Life, and it is barely enough of it to think of it as a ‘branch’; we are just a ‘tiny emerging twig’ relative to the larger scheme of things.

Today we have flowering plants, coronaviruses, ducks, ferns, fungi, paramaecia, Staphylococcus and whales and all manner of life evolving all around us. We tend to focus on ourselves, because well, why not, but we shouldn’t forget the millions of other living species on the planet and the many millions of extinct forms that came before us, some our closest relatives. But the major thing that is happening now is we are replacing that life around us with the kinds of life we prefer and that benefit us.²⁴ Most mammals (by weight) are now livestock, far outweighing wild mammals. And in fact, humans plus our livestock outweigh all other terrestrial vertebrates.²⁴ We are replacing natural selection and neutral evolution with rapid artificial selection. We aren’t just causing extinctions—we are fundamentally changing how evolution works on our planet.

PART IV

Why Understanding Evolution Matters

Evolution in the Anthropocene
(Design and CRISPR-Cas9)

I have a French Bulldog named Bessie (Figure 15). She is a rescue, because I’m a fan of places that try to save dogs and not a fan of places that make designer dogs. Although I would like to believe in a world where there are bands of French Bulldogs roving and rolling along the Pyrenees, they are in fact not found in nature. French Bulldogs, like all dogs, are descendants of wolves. Bessie is cute and sweet and an abomination. She and her short, snorty, bug-eyed ilk are an affront to her noble wolf ancestors. Her truncated snout is the opposite of what has been happening for tens of millions of years of carnivore evolution¹—something I think about when she sleeps with her head in my armpit and snores away like a tiny Elephant Man. As with all pure breeds, breeders mixed and matched different pairs, selecting the mates that would produce offspring with the same or ‘improved’ traits as their parents. (There is a reason Darwin started off the Origin of Species with examples from domestication.)

Figure 15: The Bessie.

In the case of Frenchies, they were bred to have short faces, strong stout bodies and a temperament suited for companionship.² The by-product of having their cute short snouts and large heads is that they have trouble breathing, can’t cool down well (because of short nasal passages) and best of all, they have hips too small to give birth: they are born from C-sections. In fact, the hips are so slim that the male can’t even mount a female so they must be artificially inseminated. Is that evolution? No, definitely not—but it is selection. In this case—and in all breeds that humans have moulded through artificial selection, be it bulldogs, corn or cows—it is us, not nature doing the selecting. Nature (to anthropomorphize for a moment) does the same thing, picking those organisms that best fit an environment by allowing them to survive and have offspring, while those that lack the traits for survivorship die off. Natural selection versus artificial (human) selection is just that: natural versus artificial. Nature of course changes too, year to year, season to season, and doesn’t aim with a preference of traits as we do when we select, which is why natural selection is a far slower process than artificial selection. Artificial selection is pretty slow too: you still have to wait for the animals to breed over many generations. It takes many tries to get the few individuals with the traits you desire. To speed it up, mating siblings with similar traits is often part of the process, which leads to lots of early deaths and unwanted mutations (the probability of dangerous deleterious recessive traits coming together goes way up when you breed close relatives).³,⁴ If that isn’t odd enough, we humans are taking it up an abnormal notch and perhaps taking it too far (if forced incest wasn’t enough). We aren’t just exploiting the laws of nature anymore; we are rewriting the code.

A DNA ‘typewriter’ called CRISPR-Cas (sometimes just CRISPR for short) was recently invented, and it has revolutionized the world (the inventors, Jennifer Doudna and Emmanuelle Charpentier, won the 2020 Nobel Prize in Chemistry). CRISPR-Cas is a combination of a DNA-cutting enzyme (usually Cas9 or Cas12) and special repeated DNA sequences (CRISPR) that is the genetic mechanism that some bacteria use to fight off viruses. Essentially, it can cut out strands of infectious DNA and replace it with a similar but harmless sequence that helps the bacteria ‘remember’ (so it will be ready to defend itself against that virus in the future): think of it as the bacteria’s immune system.⁵ This natural mechanism can be co-opted by scientists to do something similar: we can use it to knock out genes or modify their function to study how changes we make in the genotype (DNA sequences) can affect the phenotype (the body). CRISPR lets a scientist, or a nineteen-year-old undergraduate, change the DNA code like a typewriter that can edit or delete sequences of DNA. In that way, we can use CRISPR to speed up artificial selection. Instead of waiting hundreds of generations for desirable mutations to pop up, we can manipulate a genome directly. On top of speeding up selection, we can also change how Mendelian genetics works with another tool called ‘gene drives’ that can be used with CRISPR-Cas. With gene drives, we can make a trait act like the only version (or allele) of a gene and pass down that version to 100% of individuals, generation after generation.⁶,⁷ Will we use this new power for good or evil? What do you think? Both of course! (To their credit, the Nobel-winning scientists Doudna and Charpentier have been doing an excellent job reflecting on both the power and ethics of using their new invention.⁸–¹⁰)

Soon enough we will be using CRISPR commercially for profit. In the future we might have chickens with four or six wings to satisfy the ‘Hooters’ set. We actually already have CRISPR fruit at supermarkets that ages slower (like anti-browning apples) to improve shelf-life (and prevent waste, and of course to make more money).¹¹ Although GMO (genetically-modified organisms) are not new, CRISPR is going to ramp up the speed we see them at market. This technology has the power to solve food insecurity if used the right way, but we also have to think of the ethics of someone wanting to create new animals like a six-winged chicken or some other bogus beast. However, you could argue that broilers (meat chickens) that can barely walk because of artificial selection, which makes them very fat very fast, are already drastically different from the noble wild Asian junglefowl, Gallus gallus.*¹²

Once genomic engineering with CRISPR becomes more mainstream, perhaps a new type of bio-terrorist will create a mosquito that bites multiple times before laying eggs (it is usually just one blood meal before laying eggs for mosquitos that bite humans). That modification would make mosquitoes even more dangerous disease vectors by spreading their blood-borne diseases (e.g., malaria, dengue, West Nile virus, chikungunya, yellow fever) more rapidly and efficiently. We are already releasing ‘CRISPR’ed’ mosquitos in places where the diseases they carry are wreaking havoc.⁶,⁷ Those releases are actually done by scientists and politicians who are being cautious; although the ethics of where they carry out this work—often islands with large indigenous communities—is troubling to say the least.¹³ We can make mosquitos that are resistant to these diseases and have that trait spread to the wild with gene drives, but regulations and ethics urge caution before releasing those in the wild on a large scale. The bottom line is that we are not sure how the CRISPR or gene drive mechanism might ‘escape’ our artificially selected organism and jump (by virus) to a non-target organism. We don’t want sterile mosquito males that we release to make sterile bees, sterile spiders or sterile people.

What if an eco-terrorist decided to create a disease that killed all cows and thus removed the organism (besides us) that is most impactful in causing global warming? Or what if someone manipulated a disease that already exists in animals, like avian malaria, to jump to humans, in a similar way that coronavirus did (either from pangolins or bats) in 2019?**¹⁴,¹⁵ By the way, because we understand how it can be done, we can disprove the conspiracy theory that SARS-CoV-2 (the coronavirus that causes COVID-19) was made in a lab. None of the genetic signatures that we would expect from a manipulated virus is seen in the sequence of SARS-CoV-2; instead it is very similar to the SARS virus that already existed in wild animals before it mutated for human-to-human transmission late in 2019.¹⁵

Imagine a future where new species are created in labs and released in the same way exotic animals are released today. One need only to go to Florida or Singapore, where you can see non-native plants and animals almost as easily as you can see natives.¹⁶ Or look no further than your backyards and gardens—in the US, it is house sparrows, starlings, fire ants, coconut palms, etc., in India it is lantana, water hyacinth, African snails and tilapia.¹⁷,¹⁸ Some of our most ubiquitous ‘wildlife’ are invasives; in the future it may be CRISPR’ed life that is pervasive. I am usually an optimist, but I am a pessimist about our ability to always use CRISPR wisely. Although there are regulations in place to keep CRISPR use in check, people are already bending the rules, such as the ‘CRISPR babies’ recently born in China or the attempt of a Russian doctor to ‘cure’ some forms of deafness by modifying embryos of deaf couples.***¹⁹,²⁰ There is great potential for CRISPR-Cas to solve many of our problems, but I can’t help but quote Jeff Goldblum in Jurassic Park: ‘Your scientists were so preoccupied with whether or not they could, that they didn’t stop to think if they should.’ Having said that, the potential for using CRISPR to rid us of invasive species (by spreading a deadly mutation restricted to the invasives) or making plastic-eating plants might be the bright side of this new tech.

Before humans, there was natural selection, and it worked for billions of years. It still does, but its position is being usurped. Humans have created artificial selection by selective breeding and now by CRISPR, and we are becoming the real intelligent designers of the world around us with increasing pace and skill.***²¹ We are not just modifying the organisms that we use like cows and crops but reshaping the planet in a way that even the organisms we are not interested in also get the second-hand effects of living with us. Take trophy hunting and fishing, where we are after the biggest and most decorated (horned, tusked) individuals. Removing these trophy-worthy individuals means those traits are also being removed from the gene pool, leaving smaller less decorated individuals to breed and pass on their smaller and less decorative traits. Elephant tusks are not as mighty as they were before humans started hunting them (and tusk-less elephant populations have also evolved);²² blue-fin tuna doesn’t get as massive as they once did before they became part of the diet of the wealthy Japanese foodie.²³ Not to mention the hundreds of species we have hunted completely to extinction: passenger pigeons (once the most numerous bird on Earth), the dodo, the Tasmanian tiger—these are just the most charismatic examples.²⁴ Some estimates are that, relative to the normal background extinction rate (remember extinction is part of evolution too), humans are causing hundreds, if not thousands, of additional species to go extinct a year (many of these are invertebrates, amphibians and island species that don’t get much press).²⁵–²⁹ Most plants and animals that have gone extinct during the existence of humans are being lost because of habitat destruction, which includes pollution or removal or reshaping of landscapes.²⁸–³⁰ Some animal species have even shifted to a more nocturnal existence when they live near us.³¹ Next time you have the window seat on a flight, keep an eye out for how much forest you see versus something modified for us humans. You will likely see a tapestry of destruction. That is why many scientists call the current geological epoch the ‘Anthropocene’³² after the way we have reshaped the planet, just as a meteor or ice age may have caused a global geological shift between major periods of Earth’s history.

So what to do about it? That is for each of us to decide at a personal level. I’m not here to tell you to eat vegan or stop using straws when the solutions also need to be at an industrial and government scale. Personal choices help, but unchecked industrial pollution and indiscriminate destruction of rainforests and coral reefs need action beyond what you can do at home. It is interesting to me that in this coronavirus pandemic, with so much of humanity sheltering in place, we still haven’t made a big enough dent in pollution to hit positive climate-change benchmarks.³³ The problems are bigger than personal behaviour, but I’m also not saying we shouldn’t put in our individual effort—we just also need change at a community/governmental level. I fully admit that I don’t know how to keep an economy going or to run a business. Not all the answers can come from science or scientists, but we can provide warnings about things to come. And that’s the real purpose of this section: to explain how we are manipulating not just the planet and the organisms within it but seeing how we are changing how evolution itself works. We are altering the future of life and rewriting the rules of the past without having a clear understanding of the implications of what we are doing in the present.

Natural History

We are on the verge of changing the rules of nature with tools like CRISPR without really having a good inventory or understanding of our natural world. People tend to think of a genetics lab with white lab coats and sterile modern facilities when they think of evolution research. I think of someone wading through a swamp waving a thin net in the air collecting insects, someone looking at the behaviour of bowerbirds through binoculars or someone slipping into a cave to collect some previously undiscovered species. The study of evolution is still a lot of boots-on-the-ground discovery and what is often called ‘basic science research’ (the kind of research that is fundamental but not necessarily ‘applied’ towards some economic gain).*¹,² The products of all those boots on the ground are natural history museums (including herbariums, genetic resource repositories and other research collections) with anthropological, zoological, fungal, botanical and cellular collections. The DNA and bodies of organisms we use to study life on Earth came from people studying biology across the globe, and these collections represent our reference libraries for Earth’s biodiversity, each species a book, each specimen its own edition.³

Some people only see the potential environmental impact natural history research might make, including taking samples. ‘Taking samples’ means humanely sacrificing individual organisms to bring them back to the lab for study and to preserve them in perpetuity. These samples act as ‘vouchers’ that help verify if we have identified the specimen correctly in terms of taxonomy (i.e., if we gave it the right scientific name, so we know which species we are studying) and as evidence of the existence of the source material of the associated data which can be important for scientific repeatability (i.e., is that genetic sequence really from that individual or was it mislabelled?).4,5 As samples can be easily misidentified, and often are (taxonomy is a dying art practised by relatively few, especially in less charismatic groups),⁶ it is imperative we have a voucher to use in identifications.

We are not heartless ‘collectors’; on the contrary, natural historians are still sampling because we care about these organisms. I like explaining this work with a mantra: ‘We sacrifice the few to save the many.’ We are doing what Aristotle and Darwin did: observing and describing what we see in nature. But sometimes you need to see what makes an animal tick, and that may include dissecting them or just studying the physiology up close. Many organisms can’t be positively identified to species from just photographs or videos. Beyond that, the bodies are data; we museum folks even say ‘a specimen isn’t dead if it has data’. We keep the bodies because all the questions that we can ask today (and in the future) requires it.

There certainly are ‘collectors’ out there who want dead animals to show off their treasures, no matter how rare or endangered. Perhaps the worst of those was Lionel Walter Rothschild, whose early twentieth-century network of amateur collectors encouraged unchecked killing and caused environmental disasters for his private collections. He may have done so in the name of exploration, but that association is debatable; he certainly did not act on behalf of conservation.7,8 The work of modern natural historians is nothing like the selfish aims of Rothschild and similar collectors and trophy seekers, but many don’t see the difference. Natural history collections are so poorly understood these days that some people have stolen important and historic samples from them while justifying their crimes with the laissez-faire attitude of someone stealing a library book. And they are punished about as harshly as jaywalkers by naïve justice systems (read about The Feather Thief9 for instance). Unlike a library however, each sample in a natural history collection is unique and tells a different story about life on this planet.

So why can’t we just keep one specimen of each species? Because we need to understand variation: males, females, juveniles, breeding adults, etc. Someone might ask, ‘Are all the little toads in this ravine the same?’ We could just take a picture and a DNA sample from each and return them to their habitat, but it isn’t always so simple. Sometimes the variation is much subtler than we can predict. You don’t need all the toads to complete the story—that would be unethical—but one sample likely won’t answer your question either. No matter the question, the sampling protocol needs to be worked out and approved in advance for all the stakeholders involved (e.g., landowners and overseeing scientific and government agencies).

I work on a group of bioluminescent animals called ponyfishes (the family Leiognathidae). In several species, the females look almost identical but the males have a translucent patch (where they make their sexy light displays) that is shaped slightly differently across species—sometimes these patches are triangular, sometimes rectangular or half-moon shaped.¹⁰ Through dissecting or CT/MRI scans, you can find bigger differences internally, and it becomes obvious that these ponyfishes glow in the dark. These fish house glowing bacteria in a ‘light organ’ around their oesophagus and have mirror-like skin that helps direct the light inside their body cavities to an area on the translucent surface of their body.¹⁰ I have jars with hundreds of specimens in the fish collection I curate. I don’t feel bad about it, because almost all the ponyfish specimens are from fish markets where I picked up the already-dead bodies. They are so abundant that I usually am not even asked to pay, as they are often in discarded garbage heaps of unwanted by-catch. In fact, many of the dead ponyfishes I sample (along with lots of other low-quality high abundance seafood) are usually on their way to being ground up as fertilizer, or to become a cheap protein meal for cows and chickens or even for cat food.¹¹ These ponyfishes are collected in the millions every day throughout Asia, Australia, the Middle East and Africa. They are picked up by supertrawlers and other poorly regulated fishing vessels. Many of the birds in the collections of natural history museums (of a few hundred thousand) are from bird strikes on buildings or oil platforms where they die in the billions yearly worldwide, not to mention the billions more killed by pet cats.12,13 Natural history collections often help document the myriad ways humans are leading species to extinction, by taking evidence of those destructive practices (e.g., those bird strike specimens are labelled so we know where and how they died, and that info can help inform new window designs and practices to prevent similar deaths in the future).

Do we also sacrifice animals? Yes, but the impact of natural history sampling is minuscule compared to the wanton destruction and death we humans bring upon these species through introducing non-native species, habitat loss, overfishing, etc. Unlike those blind acts of destruction, scientists target specimens for our natural history studies and for the future work of others from an unlimited set of disciplines.³ A typical museum sends hundreds of loans of specimens and DNA samples a year to researchers studying everything from climate change to new medicines (half of pharmaceuticals are derived from nature¹⁴). We could more rapidly combat the outbreak of new diseases like coronaviruses (SARS-Cov-2) and Ebola if we had specimen vouchers in natural history collections that could help us detect the zoonotic sources of these diseases.¹⁵

A real project going on at the museum where I work includes seeing if the pollen found on mammal specimens can identify where drug traffickers are hiding.¹⁶ Collecting and storing specimens is a critical part of conservation biology, helping us understand how communities of organisms and the organisms themselves are changing over time.¹⁷ When we sacrifice specimens, we kill as humanely as possible as dictated by the strict rules of institutional animal care and use committees as governed by federal laws and the laws of the foreign, tribal and local governments where we are collecting and from whom we must obtain permits and permissions. Having said that, there is a problem of ‘helicopter science’, where researchers from Western countries swoop in collect their data and share little intellectually or in terms of resources with locals in less privileged countries: natural history has been part of the problem and helping build scientific infrastructure in the places we work should be part of the modern mission of science.¹⁸–²⁰

Why do we do still do natural history in the twenty-first century? In part to study the Tree of Life. We use the bodies and the DNA from these samples to figure out which species is related to what other species to better understand evolution. In fact, before the study of evolution, when many people didn’t even think extinction was possible, there was even more indiscriminate collecting, just for the sake of having these trophies. After Darwin, we gained an appreciation of what these animals can tell us in form and function and about our own evolution. The importance of variation and observation and the connection between species was revealed to us through the study of evolution: every individual gained value and collecting for collecting’s sake was no longer reasonable.

We also add twigs to the Tree by discovering and describing new species—I’ve described fifteen new species, and new species (both living and extinct) are added daily by researchers across the planet (about 17,000 a year; and not just boring stuff either—we get a new dinosaur about every week).²¹,²² With the knowledge from the Tree of Life, we can change scientific names to better reflect their relationships (taxonomy)** or discuss the evolution of certain traits like bioluminescence, which appeared independently dozens of times. Or we can try to figure out how we can distinguish between major lineages and note that no matter how different a peacock is from a hen-of-the-woods mushroom that, yes, we are all branches of the same tree, we all share a single common ancestor, we all came from that ancestor who lived nearly four billion years ago, what an amazing thing that all of us living things are related to one another and how amazing it is that we can study our history and that we can answer the question ‘where are we from?’ by pointing at the Tree of Life and exclaiming, ‘There!’

Our Genealogy and Ancestry

Why should you care about where you belong on the Tree of Life? Because not only does it tell you where you came from, but also who you are. As humans, we tend to see the differences between us, no matter how small, but we are all more similar than many are willing to believe. As more and more people take ancestry tests, sending their spit and money to 23andMe and other genealogy testing centres, we need to be educated on what the results actually mean scientifically, and we all have to decide together what it means socially. Many of us are coming to learn that science describes gender, race, sex and sexuality as attributes on a spectrum, but for much of our modern existence we’ve forced them into a few arbitrary, usually binary, categories. We wanted to chop up a rainbow into separate pieces instead of celebrating the fact that all our diversity comes from the same little drops of water and sunlight, each with just a little different shine. Like all species, we are defined by our differences because there are so many similarities between us. To the cosmos, we are all still just ‘star stuff’ to quote Carl Sagan; all us life forms are made up of hydrogen formed during the Big Bang and molecules like oxygen, carbon and nitrogen forged from the hearts of stars.¹ It’s what we do with that stuff that makes us special.

The more you learn about evolution and about ‘where you are from’, the more you will see our similarities. Twins can check off different boxes for race based on how they look and perhaps based on how people see them. Genetically there are just a few genes that determine eye colour and skin pigment—is that what determines your ‘race’? What does it mean when one sibling has dark skin and is treated as ‘Black’ and the other fair skin and is treated as ‘white’, as sometimes happens among mixed-race children?² I love the poem ‘Genetics’ in Jacqueline Woodson’s book Brown Girl Dreaming,³ which talks about how strangers didn’t believe her ‘pale as dust’ brother was actually related to her darker-skinned family until they all smiled, revealing the same gap between their two front teeth. Do DNA test results show your ‘race’ or family history as easily as those shared gap-tooth smiles? Not always. You can have a native American ancestor that doesn’t show up at all in your DNA test but does in your sister’s results. You might be African American but have some significant portion of Neanderthal DNA that is usually only seen at that level in people of European descent. There are hard truths in your DNA, there are mysteries and there are miracles. Your genome is Pandora’s Box, Aladdin’s Lamp, and Alice’s Looking-Glass; understanding what your genome tells you and can’t tell you (i.e., its limits) is part of understanding your origins.

We should also separate ‘ancestry’—the people who are your actual relatives and ancestors that are in your family tree—from your ‘genealogy’, which I think should refer to what your DNA can tell you about your ancestry. You probably have close to zero DNA signal left from your great-great-great-great-great grandfather, so he may not show up in your genealogy but is still part of your ancestry as a dead relative on your family tree.*⁴ The reason for the paucity of DNA from that long dead ancestor is that the DNA remaining from every previous generation is essentially halved with each generation. You got about half of the DNA in your genome from your mom and half from your dad, and your brothers and sisters get different halves (via meiosis and recombination); that means you can get about 1/4 of your DNA from each grandparent and ? from each great-grandparent, 1/16 from any great-great-grandparent and so on and so on. These are expected, or perfect, proportions; but it’s not that simple; recombination isn’t that exact, and you can lose all of that 1/16th pretty easily.⁴ (Go back to the ‘Mutants and Mutations’ chapter for a refresher on recombination; I promised you a salad metaphor back there, and here we are.)

Imagine that your genome is a salad. You get half your salad from mom and the other half from dad. Your sister would get a different half from mom and a different half from dad (imagine if their salad bowls are never empty and maintain the same composition, just tossed around before being distributed). Your family might be a family of Italian salads, but three generations ago you had a Greek salad ancestor. Your sister might end up with some feta in her salad from that ancestor, but you might not, simply due to the unique combinations of egg and sperm from which you received your DNA. So even though you have the same ancestors, your genealogy might not reflect the complete history. So it is with DNA ‘genealogy’ testing: it is limited by the mixing and loss of markers with each generation. These markers are lost because each egg and sperm cell from your parents has just one set of their chromosomes that is a unique recombined mix of the two sets of chromosomes in their other cells. The sperm and egg come together to give you two sets again, but that’s the reason you are a mix of your parents and not clones.

It is rather remarkable then that people of European descent still show about 2%** of their DNA results as being from Neanderthals, the equivalent of 1/50 or about the amount of DNA you might expect from an ancestor from six generations ago. However, Homo sapiens haven’t mated with Homo neanderthalis in more than 40,000 years (or more than 800 generations).⁵ So, there wasn’t just one Neanderthal ancestor for these people, but many. People descended from various regions of Africa also have evidence of hybridization with other extinct humans, as do people of Asian descent. All us humans also share a lot more shared recent ancestors than would be expected, even given low human population numbers in parts of our history. Frankly, there weren’t a lot of options. Even more so when you wanted to (or had to) hook up with someone of similar stock (social status, class, ethnicity, caste etc.). That means a large part of our complex backgrounds include a lot more inbreeding than we’d probably care to admit.⁶

Our evolutionary history may include some puzzling facts, but our more recent ancestry can get pretty perplexing too, especially as DNA testing becomes commonplace. In 2018, US Senator Elizabeth Warren took us down a slippery slope when she had her DNA tested to ‘prove’ she had some Native American ancestry.⁷ Native American ancestry has an important cultural link, not just a genetic one. Ancestral tribal membership is something that cannot be claimed by a simple DNA test result, or denied either.⁸ The real mistake was that Senator Warren made DNA testing a way that people think you can prove your ethnicity or cultural heritage—it isn’t. By law it isn’t: you can’t use the results of a DNA test to prove you deserve minority status for instance.⁹ It isn’t that she claimed that heritage (although she was wrong to do so, without any tribal association), it is that she took a DNA test to prove it.¹⁰ Someone with even more Native American ancestry than Senator Warren may have found no evidence of that rightful legacy from their own DNA results. These genealogy tests are good, but they are looking for specific markers of ancestry. It might be that those markers were lost through the complicated sieve of recombination.¹¹

Remember that we are all remarkably similar in terms of our DNA (<1% different between any two people),¹² so there isn’t much that makes us unique; it’s hard to find something from any one ancestor or ancestors who weren’t that different from you genetically. That’s especially true if you don’t have the full genomes of those ancestors (and there are still very few people who have their entire genomes sequenced), and we almost certainly don’t have the genomes or any of the DNA of any of those great-grandparents of yours. With commercially available ancestry tests, we are really looking at genetic markers or combinations of those markers that you share with people living today and from a particular region—those are called ‘reference’ populations.¹³ Those genetic ‘references’ don’t represent everyone in an area either, but just a few select people whose genotypes are used to represent ‘France’ or ‘West Africa’.14,15 And the people living today in a given area are not always the best representation of the past, so France or South Africa twelve generations ago looked really different than it does today (thanks to war, racism, classism, immigration and emigration).

People interpret their ‘race’ while learning genetics in some rather bizarre ways. There was a rally recently where white supremacists drank from jugs of milk, shirtless (of course), in cold weather.¹⁶ Is that their Neanderthal showing? Yes. But they were actually trying to show they had the lactase mutation that allows them to drink milk into adulthood, a trait they perceive as being part of their superior genetic constitution.¹⁷ Many people lose the ability to digest milk as they leave the breastfeeding period of infancy—we call them lactose intolerant. People from Northern Europe have a mutation that allows them to produce lactase into adulthood, perhaps a trait selected by that population when dairy products were a more abundant resource than other foods and those that could digest it were better off and had a better chance of survival and reproduction.¹⁸ But these guys (always guys) probably missed the part where their ancestors also endowed them with higher rates of celiac disease, which is maybe why they were drinking milk instead of beer.¹⁹ The white supremacists misinterpreted the lactose study¹⁸ as proof their special mutation was evidence of their Aryan superiority (not so, but good for them for reading the primary scientific literature).²⁰ West Africans also have that mutation, as do many others around the world.²⁰ Ironically, people from Southern Europe, including folks from the Caucasus Mountains, from which Caucasians are named, don’t have that mutation as commonly. These Neanderthal-men need to get their racist facts straight! (By the way, this use of meat and dairy consumption in racist tactics isn’t new.²¹)

There is no biological reality to the things we call races in Homo sapiens—it is a social construct.²²–²⁴ We are all blended shades in a tub of mixed paint. Yes, you can still see some streaks of black, white, brown and those of every colour of human, but it’s all made of the same stuff. Some ‘Caucasian’ in the US may never consider anyone from Mexico to be part of their own race. They would call them Hispanic or Latinx by default, even if they had the same ancestry, i.e., even though the Mexican and the American could both have descendants of the same European ancestors. Hispanics are just people from Spanish-speaking countries.²⁵ That isn’t a biological race—people from Spain can be Black, white and everything in between. People who are Latinx are just from Latin America, so except maybe Creole speaking Haitians and English-speaking Belizeans, all the people from primary countries that have a language with a Latin root (viz., Spanish, Portuguese) are Latinx.²⁶ Is that a race? No. Not in the biological sense anyway, but that doesn’t make them meaningless either. We do need racial categories in the US. Why? One reason is to defend people from historically marginalized groups. For instance, African Americans were enslaved, then brutalized and left unprotected by civil rights. We should try to undo some of those wrongs by maintaining some social categories for the ‘historically underrepresented’ and ‘continually underserved’ in order to protect them and slowly start the march to equality.***²⁷–³⁰ You could easily make a similar case for how the caste system in India was thought to reflect distinct ‘races’ or the way British imperialists pseudo-scientifically created Indian subgroups.³¹,³²

I am ‘Indian’ but as a ‘race’, and not a nationality, because my parents are ‘Indian’ and I was born in North America. How long do you remain ‘Indian’? Are my kids who were born in the US, whose mom is white, ‘half Indian’? Will their kids be Indian? When do you become something else? Are ‘Sri Lankans’ Indian? Someone from Bangladesh? Are we all just ‘Asian’? All 4.5 billion (4,500,000,000) of us ‘Asians’? In the US, everyone from the Indian subcontinent is labelled ‘Asian’, along with Chinese Americans or Japanese Americans. How about people from Turkey—isn’t that Asian too? Is there such a thing as ‘American’ in terms of race? Some Americans with red hats sure think so. Is my wife from Montreal ‘Canadian?’ or ‘French-Canadian’? Is she ‘French’? ‘No,’ she would say in French. When my wife tans in the summer, she can get darker-skinned than me, and so do our kids. Many people just assume we are all ‘Indian’.

Are people from Egypt ‘Africans’? How about South Africans or Kenyans? They are all in Africa, yes, but their histories are vastly different. There is no race of people who are ‘African’. Africa is a place with many ‘races’, if you want to use that term. What happens if someone from those countries immigrates to the US—do they become ‘African American’? In fact, we are all ‘Africans’ as part of the same ‘race’, the human race, whose origins are unequivocally African because all our earliest human ancestors can be traced back to that continent.

Many people who identify as African American in the US are the descendants of a stolen and enslaved people forcibly brought there.³³ They don’t usually even get to know that they have kin in Sudan or are descendants of the people from the Congo region. Their past was taken from them. They have a right to identify their ethnicity as ‘Black’ or ‘African American’, as they cannot always find evidence of their regional ancestry. The situation mirrors in some ways how Gandhi and others fought to remove the label of ‘untouchables’ while others fought to find respect by recognizing their status as an historically oppressed class.³⁴

Many people think all Africans are Black and forget the lighter skin of people from Libya, Egypt, Algeria or Morocco. In the US, they may even get lumped in as ‘Middle Easterners’. In Kuwait, which is the ‘Middle East’, most of the people I saw working there were from Bangladesh, and they are never treated as Kuwaiti even when they are born there. People from the actual Caucasus Mountains (again from where the term ‘Caucasian’ is from) include people like Armenians, who are also often dismissed as looking ‘Middle Eastern’. Why is Barack Obama ‘Black’? Because his outward appearance and how he ‘presents’, as in, how people treat him, dictated it. What about other mixed-race people—Derek Jeter, Keanu Reeves, Bob Marley, Bruno Mars, Kamala Harris. In the past, we did not have a choice—those in power decided your rights by what they considered you to be. Anyone with ‘one drop of Black blood’ was considered legally Black—end of story, as late as the twentieth century.³⁵ However, just because ‘Black’ or ‘white’ don’t pan out as distinct biological groups (and never did) doesn’t mean we get to ignore disparities in how people are perceived and treated.****³⁶ Just because races don’t exist in an evolutionary sense doesn’t mean there isn’t racism.³⁷

Sex/Gender/Sexuality

Sex is complicated, much more so in reference to the expression of physical traits than the physical act. It is perhaps even more complicated than ‘race’, and like human races we have historically pigeonholed our discussion of sex into discrete categories that don’t fit reality. Our false social abstractions often include treating sex as a synonym of gender, and sexuality with a defined ‘normal’ relegating all else as ‘abnormal’ choices or preferences. It’s time we moved our understanding forward and incorporated evolutionary science into our understanding of these very normal human traits in their full spectrum.

When I would push my identical twin babies in a double-wide stroller through a crowd of gawkers, someone would eventually ask, ‘Twins?’ ‘Yep, identical,’ I’d reply, and sometimes I’d then get, ‘Boy and a girl?’, and I would snicker internally and shake my head thinking—‘don’t these folks know what identical means’? In spite of my pretension, I was the one that had some learning to do. Later I would learn you could actually get identical twins, who have matching genomes, with different sexes (and of course with different genders too, including being non-binary). One way is that during meiosis (formation of sex cells), either egg or sperm may get two sex chromosomes rather than one, and then the developing embryos might end up with an odd number, so you can get an ‘XXY’ male (Klinefelter syndrome) born alongside an ‘XX’ female.¹ The opposite can also happen when the ‘X’ chromosome is lost in females, Turner syndrome.²

There are actually dozens of ways your physical sex (having a penis or vagina) may not match your chromosomal sex (presuming XX female or XY male).³ One way is androgen insensitivity syndrome, where you do not express the male-associated genes that are on the Y chromosome.⁴ The genes that control maleness are actually remarkably few, and they move around, sometimes even onto the X chromosome. How ‘male’ or ‘female’ (and everything in-between) you may be physically largely depends on how your hormones signal from relatively few genes, like one called SRY, which may be the most important for male sex-character development.³

The conditions described above are far more common than we previous thought; imagine if you discover you are an XX male, or XY female? I bet you don’t know your ‘chromosomal sex’ (i.e., which sex chromosomes you have). You just assume you have sex chromosomes that match what you have in your pants; you might not. So be kind to those that may express their sex differently than you expect; you yourself might have chromosomes and genes that tell a different story than you do. These simple genetic differences result in many people who are intersex (in-between male or female, in varying degrees).⁵ Research puts the number of intersex people around 1.7% of the US population,⁵ which would be roughly 5.6 million (5,600,000) Americans or about 23 million (23,000,000,000) Indians. The point of this section is the role that genes, hormones and environment may play in determining how one expresses their sex or gender. In studying life, it helps to know how much we are still learning about ourselves (and how poorly we understand and accept human variation), as a proxy for how little we know about the rest of the natural world.

Along these lines, we also have a labelling issue with a term that is more human specific; ‘gender’. Sex is one thing, gender is another: gender ? sex. Gender is how humans express themselves and their sex to the world. You might have male sex organs but identify as a woman, as one example. You may also identify outside of those binary categories. I’m not sure why people still get so upset when they learn someone is transgender or nonbinary. Is it because they may have been fooled into liking someone who they think is ‘different’? Bigots will say members of the LGBTQ+ community are not ‘natural’, but they most certainly are natural. Sex and sexuality are on a spectrum across the Tree of Life.*⁶

There are animals that seem to ‘pretend’ to be a different sex (sorry for forcing human binaries here to make a point). In some species, males have an appearance more like females to avoid competition.⁷ These ‘sneakers’ use the advantage of looking more like a female to mate with females when the big males are otherwise occupied flexing, posturing and attacking each other (‘boys will be boys’, except when they are being clever). Some will call this deception, or mimicry, but why do the females prefer the ‘feminized’ male?⁸ She isn’t being fooled.

So what’s so special about humans? Homophobia/transphobia are certainly specific to us. Some people express themselves in a different gender than the one they were assigned at birth: let’s let them live their lives in peace. Certainly, don’t come at them with some non-scientific bigotry about what’s ‘normal’. Animals don’t have genders like we do; it is a social construct of humans, so let’s construct a society that is accepting of all humanity. It isn’t ‘wokeness’, it is just kindness.

Have you watched Finding Nemo? If it wasn’t a Disney movie, what would really happen when Nemo’s mom and siblings get eaten? Well in nature, the dad would become female. Why? Clownfishes are sequential hermaphrodites—they are all born male and change to the big dominant female when it is opportune (like when big mama dies).⁹ Real life doesn’t make for the best children’s movie plots. Even in humans, your physical sex may change over time. In the Dominican Republic, there is a small community of children called Güevedoces who start out life female until about age twelve, around which time they develop penises.¹⁰ The testosterone deficiency that causes this change is common in that community but occurs elsewhere too.

More common are people who feel like they were born in the wrong body. There is a lovely book called Becoming Nicole¹¹ about a family dealing with one of their identical twin boys who from a very early age showed an intense desire to be a girl. The story is beautiful, true and uncommon only because we (at least in the West) only just recently began to acknowledge that people may have had similar feelings about their gender or sexuality; other cultures have been much more permissive, especially in places like Thailand and other parts of Southeast Asia.¹² Another interesting aspect of the Becoming Nicole story is that she is an identical twin. Both twins were assigned male at birth, and only one identified as female from the age of two. You may be wondering why, if gender identity is genetic and not a choice, did these identicals (who again have the same genome) not display the same sexual identity. One possible explanation is related to ‘epigenetics’—essentially how your genes interact with the environment. Identical twins aren’t exactly identical because of epigenetic factors, including the numerous ways certain chemicals interact with DNA (usually termed ‘methylation’); however, differences can be born out of less subtle environmental factors.¹³ If you rear your clone in a cave with poor available nutrition, they will look very different from you if you grow
up in a typical middle-class American life. Think of the genome as a blueprint to a house. The houses may have the same plan, but they will look different if one is built on an ice pack and the other on the side of a mountain. There is likely an environmental component to your sexuality and gender identity as well as a genetic component.14–16 No, the environmental component isn’t about you eating a pineapple while pregnant or singing Lady Gaga to the infant. We don’t know what the environmental conditions could be, but it is unlikely something the parents did. The fact that identicals can express different sexualities and gender identities means that there are some pretty subtle environmental factors at play and involving the interactions of multiple genes (i.e., polygenic).15,16 The Wachowskis, who created the Matrix movie franchise, are both trans women that were born as male siblings; in about 20% of cases where one identical twin is trans, both are trans.¹⁴ It is more common that identicals share the same gender identity than non-identicals, pointing to a hereditary genetic component.¹⁴

Homosexuality has been documented in hundreds if not thousands of animals.17,18 It isn’t uncommon, unusual or unnatural. My favourite example of same-sex orientation in animals that I’ve seen personally is three male elephants I encountered at a Sri Lankan preserve. The park ranger lovingly called them the ‘gay boys’. The mini-herd was made up of a thirty, twenty and ten-year old elephant (I’m not sure what the age of consent is in elephants). Usually males are solitary, but these three were always together and often . . . let’s say, ‘displaying their affections’. Who are we to tell these wild elephants how to live their private lives? Or to tell anyone really. Just be nice and accept people for who they are and hope people do the same to you.

We can observe and have observed same-sex mating across the animal kingdom,¹⁸ but gender is not so ‘straightforward’ in animals. An evolutionary biologist colleague, Jeremy Yoder,** told me, ‘You’re really not going to find a clear analogue to human transgender identity in the nonhuman world, because animals really only have gender in the sense that they have social behaviours and signals involved in mating.’ That is, it would be a lot easier to infer gender expression in animals if all you had to do is notice that a male elephant is acting like a female elephant, but most of the time an elephant is just elephant’ing and we can’t tell them apart by their behaviour. Anyway, there really is no need to force a gender binary on animals that clearly don’t have one. Which leads me to wonder—Do humans need genders? I’m not sure we gain anything from those labels. If elephants don’t need them, maybe we don’t either?

As a teenager, I worked at the New York Aquarium, where two of the male penguins would later live and be celebrated as a couple. Same-sex pairings among captive penguins are not uncommon, and same-sex penguins that pair up are often given abandoned eggs and chicks to raise. Although some are even given ‘gay weddings’, we can’t really gender them in a parallel way based on our human behaviour, nor do we need to.19,20 (On the other hand, the fact that penguins already look like they are wearing tuxedos does make their weddings pretty cute, and having these weddings doesn’t hurt anyone while serving to promote openness and acceptance.) There is no reason we would expect only binary genders in any species where we see a spectrum of sexualities.

The study of ‘gay genomics’ (‘gaynomics’?) is in its infancy. There is no single ‘gay gene’ (we’ve looked), although there may be some weakly associated genetic markers that can help identify same-sex sexual orientation. Many are afraid these investigations will just lead to additional bigotry or, in the worst-case scenario, a future where homophobic parents ‘correct’ these markers with gene-editing tools (a point made more clearly by Dr. Yoder in his work²¹). In the largest genomic study to date on same-sex experiences in humans, five genetic markers were identified, and they were not the same for males and females. The links between those genes and same-sex behaviour is very weak, i.e., there is no ‘gay gene’.¹⁶ That hasn’t stopped the ill-intentioned from producing a ‘How Gay Are You App’ purportedly based on that study; worst of all, it is distributed by a country that criminalized gay sex, Uganda.²² An app based on weak genetic correlations will only result in further stigmatizing the LGBTQ+ community. We are just getting started in this new field of study (often called Genome Wide Association Studies [GWAS] in humans), but these projects would be better served if they didn’t lead to additional stigmatizing and demoralizing. The intentions may be to produce greater social acceptance by showing particular traits have genetic origins and are not ‘choice’ or ‘preference’, but these studies can be co-opted with awful consequences.

GWAS studies have also been conducted to try to find genetic links correlating to income level²³ and educational achievement.²⁴ I understand the motivation for finding correlates in newly available genomic datasets (‘it’s information, it’s science’), but there is also a great need for a proper context to explain the significance of weakly associated loci that are attributed to features that are found on a gradient (e.g., race, socioeconomic status). Poverty, for instance, was thought to be among the heritable traits that American eugenicists wanted to eliminate with forced sterilizations.²⁵ That is part of the reason we need better science communicators and to find scientists who can communicate complex social issues. Even Aristotle divided his writing into the ‘exoteric’ and an ‘esoteric’, the former for explaining his ideas to the average person and the latter reserved for his fellow philosophizing pedants and preeminent peripatetics.***²⁶

What does all this have to do with evolution? Some people ask what the natural-selection explanation for same sex attraction might be. After all, same sex couples can’t make their own babies and will not pass down their traits to the next generation (although science is working on it). We don’t have similar evolutionary discussions when bringing up the thousands of people who kill themselves before having children because of depression, anxiety or other heritable illnesses.²⁷ That’s because there isn’t the same kind of bigotry related to those illnesses as is thrust upon people who identify as Lesbian, Gay, Bisexual, Transgender, Queer/Questioning, Intersex or Asexual. Of course, being attracted to the same sex isn’t an illness, but there are people who suddenly become scholars of natural selection and invoke Darwin’s name in vain when they expound their genderist/heteronormative bigotry against the LGBTQ+ community. Even asking the question of why same-sex sexual behaviour exists in an evolutionary context assumes that ‘normal’ is different-sex sexual behaviour, and that shows some ignorance about what ‘normal’ sexuality is on the Tree of Life.²⁸ The truth is you don’t need a biological explanation to treat people with respect.

Evolutionary studies on human sexual orientation are difficult to conduct because so many people live in fear of truthfully expressing their own personal feelings because of the prejudice they might face, although about 3.5% do self-identify as gay, lesbian or bisexual.²⁹ (That is about 9 million [9,000,000] Americans or nearly 50 million [50,000,000] Indians. For a perspective on the LGBTQ+ life and history in India please read Queeristan by Parmesh Shahani.³⁰)

One hypothesis for the existence of same-sex sexual orientation is that some of the genes for this trait may be passed down by people with a spectrum of partners, including cases when they pick an opposite-sex partner with whom they produce children.³¹ There is also evidence that the genes for same-sex sexual orientation may be carried and passed down by relatives who are ‘straight’ (i.e., different-sex sexual orientation) and who carry these genes but do not express ‘alternative’ sexualities themselves. For instance, there is evidence that the female relatives of gay men have more children, which would lead to the trait persisting, as these more fecund women pass down those ‘gay-ish’ genes even if they themselves are strictly heterosexual.³² In that scenario, the loci influencing same-sex sexual orientation would express themselves differently in these women and be passed from generation to generation by the straight (or at least the baby-making) relatives.³³ You can imagine this system leading to more help for these fecund mothers from relatives who do not have their own offspring; those non-reproductive ‘helpers’ in these scenarios are conjectured to be predominately gay.34,35 Think of all those gay uncles, ‘guncles’ as one of my friends refers to himself to my twins. These scenarios are actually a little too simple and convenient in my opinion; ‘more science please!’

What we do know is that sex, sexuality and gender identity are not as fixed to each other as we once thought. Not only do people have a wide variety of sexual orientations in terms of who they are attracted to, but many people are also born intersex in a multitude of ways. There is variation in humans, and although many societies have created social norms including binary categories for gender and sex, we know that those categories do not cast the net of human variation widely enough. We need to do better, we need to educate each other and use inclusive language, and we should be informed by the latest science to do so.³⁶ We should also not let misinterpretation of that scientific information lead to policy decisions that restrict freedoms based on traits we know are natural and variable.

Box 2: Sexual Selection or Something Else?

We’ve discussed sexual selection several times in this book, first as an idea Charles Darwin used to explain the extreme or gaudy traits members of one sex of a species sometimes possesses, e.g., the peacocks long and bright tail feathers.¹,² These features may hinder the peacock’s ability to avoid predators but will improve the male’s chances of mating with peahens. Darwin also used sexual selection to explain the differences in human sexes, including why males tend to be larger than females in our own species. He thought human males compete for women and thus needed stronger and bigger bodies to fight competitors, saying:

There can be little doubt that the greater size and strength of man, in comparison with woman, together with his broader shoulders, more developed muscles, rugged outline of body, his greater courage and pugnacity . . . these characters would, however, have been preserved or even augmented during the long ages of man’s savagery, by the success of the strongest and boldest men, both in the general struggle for life and in their contests for wives; a success which would have ensured their leaving a more numerous progeny than their less favoured brethren.²

Darwin’s explanation hasn’t been called into question as frequently as one would expect; recently a biological anthropologist, Dr. Holly Dunsworth, discovered an alternative explanation that doesn’t require old gender stereotypes of savage men and small meek women.³,⁴ Dunsworth found that the differences we see in height and pelvic width in humans can be explained by simple hormonal differences. People producing oestrogen from ovaries will be shorter and have wider hips; human bone growth relies on this hormone and greater production by ovaries earlier in life (versus those lacking ovaries) explains physiological differences that have previously been almost exclusively attributed to sexual selection. Dunsworth’s physiological explanation doesn’t require a Victorian-age male-on-male competition story to explain size differences between human sexes.

Although it can sometimes be overemphasized, sexual selection theory is extremely valuable for explaining the variation we see within and across species.⁵,⁶ It rests upon the fact there is competition among the sexes for limited resources (e.g., eggs are less abundant than sperm in most animals). We tend to describe sexual selection as just male competition, but it is more often better described from the view of ‘female choice’. Think of it as the relatively limited egg-producing females selecting their choice of mates among the more plentiful sperm-producing male resources; that’s why males need flashier coloration or create more decorative nests to attract females (and yes, to sometimes fight amongst themselves too). There are also times males are the limited resource and are the choosy ones, such as in pipefish males choosing larger females as partners because males carry the developing eggs and so become the limited resource; or as in the bright plumage of combative female red phalarope (Phalaropus fulicarius), in which the dull-coloured and smaller males dutifully incubate the eggs in her territory even after she flies off to begin her migration.⁷,⁸ Sexual selection is a powerful tool for explaining diversity on the Tree of Life; taking a view that isn’t skewed by our own biases may improve our understanding of its role in evolutionary biology.

Combatting Post-truth with Trust

We live in the ‘post-truth’ era. People can say what they want, and some people, especially their followers, will believe it. I don’t think you can combat ‘post-truth’ with truth—people will believe what they want, and we all have our own truth. What we need is trust. People believe those they trust. Maybe you believed in Santa Claus because you trusted your parents or in ‘trickle-down economics’ because you trusted Ronald Reagan. I trust in science because I learned how to be a scientist from people who taught me to discover and explore on my own. From carrying it out, I learned to trust the scientific process.

I had an undergraduate student in my class once who didn’t believe the moon landings happened. I could have given her all the scientific papers that resulted from the lunar landings or shown her how we still use the reflectors left behind on the moon to measure distances using lasers, but I know she would have remained unconvinced. If the videos are fake so is everything that comes with it. What I had to do was gain her trust, get her to trust science and to show her how to discover the truth on her own by finding and understanding the available research. I hope you do that too, and don’t just drop out of class like that undergrad did. If you think about it, you also probably believe the moon landings happened, or that COVID-19 kills, because of who you trust. Same for the subject of evolution. Have I gained your trust yet?

What I teach in my classes are not just parades of facts that I expect the students to regurgitate during an exam. I show my students how to look up and understand scientific literature and to make up their own minds. Teach a student a fact and they have food for thought for a day; teach them to find facts and they can educate themselves for a lifetime. Sorry for that awkward version of the classic ‘give a man a fish’ proverb, but I find that a fact a student finds on their own is a hundred times more valuable and memorable than if I just tell it to them.

Of course, scientists have opinions too. Our job is to remove those opinions and biases from our work as best as we can and let the data speak for itself. As I mentioned in the beginning of this book, teaching evolution helped me realize that this topic remains controversial because of trust. And you can’t have people trust your data without them trusting you and the scientific community at large.

Scientists aren’t perfect, and pursuing truth is sometimes easier than earning trust for us. Some of us act like we are the sole purveyors of truth and that all scientists should be trusted; however, as in all professions, there are some bad apples in the bunch. Some scientists have pushed others out of the field by crossing the line between helpful critiques and unfair criticism. These are often doled out in a biased fashion against colleagues who are more junior or from underrepresented groups.¹ We scientists also need to improve communications between colleagues but also better incorporate (not ignore or assimilate) knowledge of local and indigenous people into our science: Dr. Andrea Reid and others call this use and incorporation of both indigenous and mainstream science ‘Two-Eyed Seeing’.2,3 Incorporating locals into the scientific process as a part of citizen-science campaigns (sometimes called ‘public participation in science’) can also increase people’s trust in science and scientists, as can other interactive scientific outreach.⁴–⁶ Perhaps a larger issue is that it often appears that just wealthy countries and wealthy people do science. We need to build scientific infrastructure and reach out to communities where people can’t (or won’t) come to universities or museums to show that science is not just for the privileged. We’ve done a poor job of creating an inclusive and welcoming environment in science and of fostering diversity in fields that study diversity. But before we can spread knowledge, we need to earn trust.

How do you earn trust? I don’t know if there is a rule book that works for everyone, but I do think one-on-one personal communication and listening can help. Also don’t do things that would make someone lose trust in you, because it is nearly impossible to get it back.

I happen to like meeting new people, which is a nice trait to have for gaining trust (and probably linked to being trusting). I like to listen to them as they explain to me what they do and how they got there. I’ve met security guards, real-estate agents, moms, dads, billionaires, the unemployed and everything in-between. Listening to their stories and acknowledging their backgrounds, hardships and passions can help gain a mutual sense of trust, especially if you are also willing to be open-minded and open-hearted.

The folks I meet sometimes ask me what I do, and I say some version of ‘I’m a dad of twins and a husband, and I teach evolutionary biology and I’m a fish curator at Louisiana State University’. Usually I get a ‘that’s cool’. Then we talk about sports or something along the lines of ‘what’s a fish curator do?’ Sometimes, not always, I get: ‘Evolution—isn’t that just a theory?’ Some folks are locked and loaded with that one. The rest of the conversation usually goes something like what I have in the next section. I don’t try to change people’s minds during these conversations. If they are coming from a religious perspective, nothing short of a collapse of their worldview would be required for them to accept evolution as explaining their origins. And that is true of me too—my worldview would have to change dramatically for me not to accept scientific doctrine. When I’m trying to gain trust, all I do is play defence and try to explain as a teacher what evolution is and what it isn’t. I am not trying to indoctrinate anyone; it doesn’t matter if this particular person understands science or not. I’d like them to, and I will try to find common ground, but I never have an argument, just a polite conversation. And I do try to gain their trust. I hope the hypothetical conversation below can be somewhat instructive, if nothing else. It is composed of real questions or online comments I’ve gotten over the years.

Comments from/Conversations with/Creationists

It would be nice if conversations would work like what I’ve written below; it is unusual these days for anyone to get to finish their thought before being interrupted. I hope the real conversations you may have can be so constructive.

Meet average citizen ‘Joe’ and hypothetical ‘Pro’,—who is me, but more articulate. They are closing out a quiet hotel bar. After having exchanged pleasantries watching baseball on the TV, Joe asks what he’s been itching to ask ever since learning of Pro’s profession a few minutes earlier.

Joe: ‘So, umm . . . isn’t evolution just a theory?’

Pro: ‘Well, frankly, no, it isn’t. Evolution is a fact. Everything we can observe about it points to the fact that life on Earth has changed, in other words (*throws up air quotes*) “evolved”, one from another, all from a common ancestor about four billion years ago. The evidence includes everything from fossils, to the shared DNA of all of life, to the modified limbs and organs that make up our bodies.’

Joe: ‘So why is it called the “theory” of evolution?’

Pro: ‘There are lots of theories of evolution. The one that people are most familiar with is ‘natural selection’: that’s the one that Charles Darwin came up with. There have been other theories, some right, some wrong. But none of those ideas about how evolution works changes the fact that life on Earth evolved.’

Joe: ‘So what’s so special about Darwin’s natural selection? Why is that a theory?’

Pro: ‘Well, I think we are using the word “theory” differently. Scientists don’t usually distinguish between “theory”, “law”, “fact” in the same way we do in everyday conversation. Saying “theory” doesn’t mean that the jury is still out. That’s why I like using “fact” in everyday bar parlance. Not that I’m in a bar every day . . . sometimes I drink at home.’

Joe: ‘Nice. Me too. But I don’t get it man, tell me where you think we came from.’

Pro: ‘See, we are humans, that makes us apes, mammals, vertebrates, a small twig on the Tree of Life.’

Joe: ‘The Tree of Life?’

Pro: ‘Sorry, yes, the “Tree of Life” is the depiction of all life on Earth, living or extinct, showing how we organisms are all related to one another. So we are “apes” because we are in the part of the Tree with other ape species.’

Joe: ‘I don’t quite get it. Why are we apes? I don’t think I came from a gorilla, although the hair on my back is pretty silvery these days.’

Pro: ‘Fantastic, thanks for sharing that. [*Sips from Manhattan. Picks up pen and draws remarkably neat phylogeny of primates (like Figure 4) on a bar napkin as he talks.*] We didn’t come from gorillas specifically, but we are apes. We share a common ancestor with chimpanzees from a few million years ago. And with gorillas a few million years before that. Chimps are our closest living relatives, but there were almost a dozen other “human” species that were more closely related to us that went extinct. If they were around, you could more easily see that transition between us and the rest of the apes. Where do you think we came from Joe, if I may ask?’

Joe: ‘I was made in God’s image, just like the [insert religious text] says. What religion are you?’

Pro: ‘If it is okay with you I’d like to keep my religious beliefs out of this conversation and keep my answers about our origins strictly scientific, at least on my side. Since you are asking me about the science of evolution and all.’

Joe: [Sips beer, looks up at baseball game showing on the screen.] ‘Don’t you think all that you study is wrapped up by human perception, I mean we were not here millions of years ago, so we have to make sense of old bones and make up stories. No one has seen those fossil humans walking around.’

Pro: ‘That’s what humans did for a long time, yes. Make up stories based on what they saw from the past. Maybe not unlike: “God creating people in his image, and in return people created God in their image.”’

Joe: ‘So you are saying I’m right?’

Pro: ‘I’m not here to tell you that you are right or wrong. But as human culture changed, we created more sophisticated tools to test those stories from the past. We can use DNA to place ourselves on the Tree of Life, and we have fossils of other humans that we can compare the bones with other apes and animals. We even have the DNA from some of those fossilized extinct humans like Neanderthals and Denisovans.’

Joe: ‘Denny-who’s-van? You making this stuff up man? How do you get DNA from fossils?’

Pro: ‘It’s interesting. There are lots of human fossils in part because apparently some of our close relatives liked to hide out, live and be buried in caves.’

Joe: ‘You mean like Bin Laden or something.’

Pro: ‘Yes exactly [*laughs with a smiling Joe*]. Some of those extinct human species died out recently enough that their bones didn’t turn to stone yet in those caves. They didn’t fully decompose so we could get DNA out of it. That’s why we can tell that people of European ancestry have around 2% Neanderthal DNA as part of their genome, and people of Asian ancestry have more Denisovan in them. Have you taken one of those DNA tests?’

Joe: ‘Not yet doc, but I’m planning on it, except I know I’m 100% American baby!’

Pro: ‘That’s right man.’ [Clink glasses, break into ‘USA! USA!’ chant startling the other bar patrons. Pro does not reveal he was born in Canada.]

Pro: ‘There are so many weird paradoxes. A lot of people think we humans have the most DNA, or the most genes, but it’s much more complicated. If you stretched out the DNA in just one of any of our cells, it would be about as tall as we are; but if you took all the DNA from an amoeba, which only has one cell, the genome would be taller than this building. Rice and mice and some parasites have more functional genes than us. It’s crazy.’1,2

Joe: ‘Okay, so our DNA might not be all that complex compared to slugs or whatever. Tell me this though: can you name a species that has evolved from natural selection?’

Pro: ‘How about Homo sapiens, our species. We had to struggle and compete with other species (including other human species), that probably led to our bigger brains, advanced language skills, maybe even to innate beliefs in a higher power.’

Joe: ‘You think we beat out those other species because we believe in God?’

Pro: ‘Not necessarily a particular God, or gods, but shared belief system maybe gave us an advantage over other human species that perhaps were solo or in smaller family groups. But now I’m fighting above my weight class a little bit. Let’s just call that one of the theories of human evolution.’

Joe: ‘You teach all that stuff to college students?’

Pro: ‘I show them these ideas and I try to provide as much evidence as I can to let them make up their minds. I’m not telling them to believe me—they can believe what they want. My job is to teach them what the available science is and to show them how to find that evidence, or at least research about that evidence, on their own.’

Joe: ‘So how does one find that scientific info?’

Pro: ‘Glad you asked. You got your phone on you?’ [**Eats one of the cherries out of his nearly finished drink.]

Figure 1: My ancestry test results. The percentages are real (taken with a grain of salt), the historical figures I’ve assigned are a fiction of who I’d like to be descended from. Yul Brynner is representing his ‘King of Siam’ character not himself (he pretended to be Swiss/Japanese but had mostly Russian ancestry). Alexander the Great left no direct line (his son was killed before having his own children) and although every Asian thinks they have some Genghis Khan in them, we won’t know without some DNA link to his actual descendants—which we don’t have.

Figure 3: The ‘Vertebrate Tree of Life’ is the same as the ‘Fish Tree of Life’ (since you can call all vertebrates, ‘fish’—because of our shared ancestry); tetrapods in the red and dashed area (represented by a hen, but you belong in there too—along with other mammals, birds, reptiles and amphibians) as part of the bony fish lineage; specifically you are a lobe-finned fish (of which lungfishes and coelacanths also belong). Things we typically call ‘fish’ are in blue (with gills and fins), and the red portion of the tree is just the group mainly found on land (and who have modified gills and fins as you do).

Figure 4: Relationships of living and extinct human species: chimps are our closest living relatives, but there were other species that were much closer to us in the past.

Figures 5A and 5B: Two depictions of the Tree of Life. (A) phylogeny with molecular evidence from Hug et al. 201615; (B) simplified version showing major divisions.

Figure 7A: Evolution is the process that connects all life. The connections between life on Earth are often depicted as a tree-like form (as in Figure 5). But you can also imagine it as more of a web showing an unbreaking sprawling series of interconnected ancestor-to-descendant relationships (as in the top figure)1. Importantly, extinction isn’t depicted here (but see Figure 7B). Starting from the first life, represented by a single cell (with the white egg-shaped centre) expanding into more, new types of unicellular life represented by the other circles (with no holes in the center), each a different species (steps #10 to #9). That unicellular life keeps evolving, but multicellularity also (step 8) with fungi, plants and animals gaining that trait in their respective parts of the web (multicellularity would evolve multiple times independently). If we focus on just the animal part of the web, we get a diversification of vertebrate life represented by fishes (step #7), and if we follow the vertebrate line you can see that fishes continue to evolve and diversify, but that one fish lineage expands and gives rise to the line that results in mammals including us humans (step #6’). However, as we evolved, so did the rest of life (full step 6), with more unicellular forms too, all diversifying and evolving into the complete web of life (step 6). We tend to just focus on our line of descent (as in the new portion of #6’), but the entire history is much more complex.

Figure 7B: What is missing from Figure 7A is extinction. Step #5 here shows that the earliest life forms gave rise to other life but went extinct along the way (the hole in the doughnut). There may be some fossil remains or other elements, but the centre of this web of life is very old and has left hardly a trace except the descendants, depicted as the younger outer ring, and a few fossil remains (the individual species inside the ring). The scattered life around us today (#2) is just a fraction of all the life that has existed on Earth. Throughout human history, we tend to line up that life with what we see as the most advanced, namely ourselves, as the end of the line, with those we see as more ‘primitive’ forms following behind (#1): that evolutionary line we picture is nothing but an artificial construct, and maybe it is all Aristotle’s fault for getting us to think that way in the first place (see Figure 6).

Figure 8: Natural Selection—Step 1: Make babies; Step 2: Babies struggle to survive because resources are limited, some die off; Step 3: Babies that prove to be best fit by surviving into adulthood make more babies. In this case, blue fish with spots are best fit and grow up to make more blue-spotted fish. Note that all the variation is not lost, a change in the environment may favour red fish with stripes or yellow catfish next season.

Figure 9: Crossing purple pea flowers yielded ¾ purple flowered plants and a quarter white. Why? Mendel deduced there were pairs of what we now know as genetic alleles that separated during reproduction (the dominant ‘B’ and recessive ‘b’). Whenever big ‘B’ was present a purple flower appeared and little ‘b’ was just from the ¼ of the time there was no big B in the combined seed. What this experiment did is show us how to separate the genotype from the phenotype to explain the maintenance of variation.

Figure 10: An explanation of the ‘deck of cards’ metaphor for recombination. Your parents each have twenty-three pairs of chromosomes (forty-six total). Each egg from your mom and sperm from your dad has half the set (twenty-three total). To make a sperm/egg via meiosis, the parental set is ‘shuffled’ via genetic crossover, where pieces from the different sets are recombined. During this recombination, the deck is split into half, so that only one half of the recombined chromosomes is in each sperm and egg. The egg and sperm come together during reproduction, bringing the total number of chromosomes back to forty-six. As recombination takes place, some mutations will be lost (beneficial or not), but this process also creates the unique combination of features that make you and your siblings different from each other and from your parents (in addition to the unique mutations that you gained in this process). (Please note that the process of meiosis from which sperm and egg are made is far more complicated than summarized here.)

Figure 11: A meandering river (I.) has an adjacent population of rodents; the river eventually makes an ox-box lake (II.) the population of mice within the ox-bow lake is cut-off from the rest of the population. It is slightly more humid and cooler on the island, and there are fewer hawk predators but also less food and nesting spots. It is also muddier, leading to natural selection for darker fur to camouflage better. Eventually the river returns to its normal shape (III.) but not before the rodents have accumulated enough physical and genetic changes to be considered distinct species.

Figure 12: A hypothetical example of speciation. Species ‘A’, like all species, is made of different individuals, and like many species is made up of populations in different areas (left side). If separated by a barrier (such as the icy-blue and pointy mountain range) for a sufficient period, the populations may diverge into distinct species (‘B’ and ‘C’). The difficulty is knowing how much change is needed for speciation. It takes place somewhere along the branches from A → B, and from A → C (bottom right). The changes that accumulate during this separation don’t need to be adaptive— they can be neutral changes to the DNA. Ultimately, there can be enough changes to reduce the likelihood of gene exchange even when the now-different species can mingle again (bottom left). These accumulated changes could also include things like new phenotypic differences and preferences in characters of mates, so that the blue color with ‘x’ markings is favoured among members of species C, so they don’t attempt to breed with the purple-coloured and spotted species B. Or perhaps enough genetic differences arose between members of B and C that, even if they attempted to mate, they could not produce viable offspring.

Figure 13: The old tattered ‘Book of Life’. Many pages are missing including the introduction that explain the origins of life. Some pages have been shuffled back in, and it remains largely incomplete. Living species are well represented and they make up the pages at the end of each subsection that reflect the major classes of life on Earth. Although major taxonomic groupings are a bit arbitrary, from largest to smallest they are: kingdom, phylum, class, order, family, genus, species. We humans, Homo sapiens, are the last remaining species in the genus Homo, of which there are nearly a dozen extinct species, such as Homo neanderthalensis, the Neanderthals. The other members of our family include chimpanzees and orangutans, and our primate order includes monkeys and lemurs. At a higher level we are members of the class of mammals—with dolphins, platypuses and wallabies; we can identify with hagfish and sea squirts and all vertebrates that at some stage have a nerve cord, a notochord, pharyngeal gill slits and a post-anal tail that make us members of the phylum Chordata; and finally, we belong in the kingdom Animalia with all the other animals.

Epilogue

This book is titled Explaining Life Through Evolution, and I wanted ‘life’ to mean ‘all of life on Earth’ and maybe also your individual ‘life’. So it seems fitting that I’m finishing up writing this in ‘The Age of Corona’, when we are thinking about the fragility of our own lives in the greater scheme of things . (Remember too, the holistic approach of biology I coined as ‘ayurvedology’ in the beginning of this book.) On 10 August 2020, former US President Donald Trump stated, ‘This is a very brilliant enemy. You know, it’s a brilliant enemy. They develop drugs like the antibiotics. You see it. Antibiotics used to solve every problem. Now one of the biggest problems the world has is the germ has gotten so brilliant that the antibiotic can’t keep up with it.’¹ Now Donald and I are just a couple of guys from Queens; but he is a businessman, and I am a biologist, so I don’t expect him to know as much biology as I do. I do hope he can be taught that antibiotics are for bacterial infections and that viruses are not bacteria. If you put that aside for a moment, his point is actually an evolutionary one. ‘The germ has gotten brilliant’—yes, it gets more ‘resistant’ by evolution, natural selection. Even with a vaccine, we will still need to be cautious as the virus evolves.² Those viruses that could not withstand anti-virals (in a vaccine) would die, and those that survive make copies of themselves that would also survive, i.e., they become resistant to the drug.² Some survive and some don’t because of the variation in the virus’s genetic code.

Apparently, the President was advised by a legal scholar who also mixes up bacterial diseases like syphilis with viral diseases like AIDS.³ The source, Richard Epstein states: ‘I’m taking standard Darwinian economics—standard economic-evolutionary theory out of Darwin—and applying it to this particular case.’* Now unlike the President, this advisor states he ‘worked on evolutionary theory for forty years’. He is pointing at the decreased virulence of diseases over time, to point at the fact that SARS-CoV-2 should kill far fewer people than projected (at first, he said only 5,000 would die⁴—at the time of writing it is approaching 1,000,000 deaths in the US and over 5 million (5,000,000) dead worldwide, and still growing, not to mention all those undiagnosed patients and deaths⁵). Some models predict that it benefits most viruses to be less virulent over time, because if you kill the host you stop the spread of your copies, rabies being a major exception with its near 100% mortality rate in humans.⁶ The problem is that this coronavirus is changing very rapidly and spreading very quickly and has a mortality rate already in the single digits (about 4%, or four times higher than the flu).⁷ Unlike the 1918 ‘Spanish’ flu which killed perhaps 100 million (100,000,000) people, many of whom were twenty to forty years old,**⁸ this new disease is targeting the old and generally sparing the young (although look out for the variants such as Omicron).

The fact is that it is still too early to know how the virus is going to evolve. It may become more virulent; that’s part of why we are all hiding inside and wearing masks, because at least we know how a coronavirus spreads (although some of us are also acting like ‘germ theory’ is ‘just a theory’ to use the unfortunate common parlance).***⁹ We can even track how this virus is spreading by looking at how it changes in its hosts (that’s us) over time, and because it evolves so quickly we can see it change in near real time on a phylogeny (a little disheartening to watch but nextstrain.org is tracing the tree of SARS-CoV-2 on a daily basis). For instance, from the phylogeny of this coronavirus we can see that most of the initial infections in New York actually came from multiple invasions from Europe and not from Asia.****¹⁰

The problem with equating viruses and bacteria as the former President and Mr. Epstein have done is that viruses are very sloppy at copying themselves (RNA to our DNA back to RNA), and that allows lots of mutations—enough mutations that the immune response that we have might not be able to recognize a new version (i.e., you can be re-infected and get sick multiple times). Coronaviruses (if not this specific version of SARS-CoV-2) have been, and will be, with us for a very, very long time. In fact, coronaviruses are common—they include some of the viruses that cause the catch-all ‘common cold’.

Just as we need a flu shot every year, we might need to get one for ‘the rona’ too and for the same reason. The flu changes and morphs (read: it evolves), and if you don’t have a prior history with it, you get very sick and even die as tens of thousands do each year. Right now, COVID-19 is one of the leading causes of death in the US. In the face of that fact, some people argue that we should let people die from diseases to allow the fittest to survive (they are thinking of actual physical fitness, not reproductive success as evolutionary biologists use the term ‘fittest’); except in that case they are the ones who decide who is ‘fit’ (clearly they do not mean the immune-compromised, frontline health workers, or the poor). So that’s actually artificial selection, if not straight-up eugenics. Those are the folks throwing peanuts at the kid with the allergy or stomping on your glasses or coughing on nurses.

President Trump has discussed what he called the ‘racehorse theory’ when telling a nearly all-white crowd, ‘You think we’re so different? You have good genes in Minnesota.’ He also praised American industrialist and Hitler’s hero, Henry Ford, for having ‘good bloodlines’, both statements being closely tied to eugenics and anti-Semitism.11,12 It isn’t clear to me how the Indian Prime Minister, Narendra Modi, understands biology either, as he suggested the Mahabharata included examples of stem-cell technology and plastic surgery and members of his Bharatiya Janata Party also promoted eugenic-themed pseudo-science.¹³ How do you think these folks will use technology like CRISPR on human embryos? Or use your genetic information in health screenings that determine your medical coverage or academic ability? So yes, understanding evolution matters—your life, and our future, may depend on it.

* See also ‘Edwards v. Aguillard’, a 1987 case where the Supreme Court struck down a Louisiana law to teach creationism alongside evolution.

** Read more about that remarkable LTEE experiment in the Lenski lab publications.¹⁶ Sadly, the LTEE experiment was paused for the first time after thirty years (!) due to the COVID-19 pandemic; it was restarted after a six-month hiatus in September 2020.

* I do have a hypothesis that identical twins raised together are actively trying to be different from each other, while those raised apart are more similar in dress and disposition (look up the ‘Jim twins’ or ‘Three Identical Strangers’ for example). A sort of ‘character displacement’ (where similar species accentuate their differences in close proximity) takes place among twins raised together. Hit me up if anyone wants to carry out this study with me (ethically of course; we won’t be separating families). By chance we had a second set of identical twins with us at the time of this writing—three-year old boys that we were fostering—who only reinforced my hypothesis.

** Rest in peace to Dr. Lewontin who also died in 2021, along with his Harvard colleague and nemesis E.O. Wilson.

* I was surprisingly pleased to see that my kids had a homework assignment (third grade public school class in Baton Rouge) that had them distinguishing between heritable and acquired traits. Times may have changed, but there is still much progress to be made.

* Walk into any public university library, and the staff will help you find primary resources too in those stacks of journal articles in bound volumes. For evolutionary biology, check out the journals Evolution, Systematic Biology, Nature, Science and many others that are also online. Again, I recommend you start by searching in ‘Google Scholar’ https://scholar.google.com/.

** That quote is from perhaps the twentieth century’s most well-respected evolutionary biologists, Ernst Mayr, in his book What Evolution Is,² which was published when he was 97 (!) in 2001. (That book is dedicated to Aristotle, and I remember wondering if it was possible that they knew each other, so long and storied was Mayr’s career.)

* Don’t come at me Newton fans with talk of Principia—no one reads that original text anymore, and few did then⁹, but people still read and reference Origin of Species. Unfortunately, we don’t have as much information about non-Western thought on biological evolution. It would not be surprising if natural selection had independently been discovered in China, India or western Africa. There is some evidence that the great Iranian scholar Abū Rayḥān Al-Bīrūnī may have also thought up a process of evolution via a struggle for existence, but he didn’t write much on the subject. Read S. Frederick Starr’s excellent Lost Enlightenment¹⁰ for a beautiful scholarly take on some discoveries from Central Asian scholars on space, time, religion, medicine and the natural world that pre-date or parallel that of the West. In the first century, an Iraqi scholar, Al Jahiz, wrote The Book of Animals that also had pre-Darwinian evolutionary ideas.¹¹ Rebecca Scott does an excellent job explaining his contribution along with others’ that influenced or pre-dated Darwin in Darwin’s Ghosts.¹² The contributions to early natural history from non-Western scholars is something worthy of more lengthy discussion than I provide here.

** Read Carl Zimmer’s excellent book She Has Her Mother’s Laugh,¹³ where he gets into some of the details of Darwin’s ‘gemmule’ hypothesis on how heritable traits are physically passed down. With gene editing tools like CRISPR and gene drives, perhaps Darwin’s genetic hypotheses and even Lamarckian evolution are becoming realities—more on that in Part IV. For the full scientific treatment, I recommend you read Mary Jane West-Eberhard’s Developmental Plasticity and Evolution,¹⁴ which provides a detailed academic examination of the ways variation in the phenotype plays a role in speciation and evolution.

* Is Mendel’s understanding of what he discovered a little overstated? Perhaps⁴,⁵. He is a convenient hero, but the work has stood the test of time. Even scientists love to reinforce the mythos of our forgotten tragic heroes and of the unrepentant evil bastards of history. Still, I’d put Mendel’s insights up there with Einstein dropping relativity on the world while working as a lowly patent clerk.

** The explanation of Mendelian genetics I use here can be found in nearly every introductory biology textbook.⁶ Mendel was lucky to work on peas with ‘discrete’ features (like flower colour) that segregated nicely. Unlike easy-peasy peas, bees have a much more complicated pattern of heritable traits (read up on quantitative genetics of continuous traits), which is why Mendel, as the proto-geneticist beekeeper, didn’t deliver any scientific discoveries.¹⁰ (That must have really stung.) Like many failed academics, he went on to a life of obscurity as an administrator.

* At least no more random than death.

** If you don’t like cards you may prefer the salad metaphor that I use later to explain a similar consequence of recombination.

*** This the often-paraphrased version of the German physicist Max Planck’s quote in his 1950 autobiography—‘A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.’²⁵

* Galapagos finches is a group Darwin did not cover very much in his own writing⁷ but subsequently became a model example of adaptive evolution. It was other biologists back in England who helped Darwin recognize that the little birds he carelessly labelled (not even keeping track of which island they were from) were different kinds of finches, but Darwin did recognize that they would have had a single ancestor on the mainland. Check out Rosemary and Peter Grants’ work on these finches that should be called ‘Grants’ finches’, not Darwin’s, or read about the Grants in The Beak of the Finch: A Story of Evolution in Our Time by Jonathan Weiner.⁸ Notably, thanks to their habit of stealing food from tourist traps, some Galapagos finches may all be evolving to prefer French fries (I don’t know what their beaks will look like in a thousand years).

* There are publications on this topic, but I think Lauren Sallan’s 2017 TED talk is the best explanation of how life today is made up of the winners of past mass extinctions. https://www.ted.com/talks/lauren_sallan_how_to_win_at_evolution_and_survive_a_mass_extinction

** Agassiz was a terrible racist, and his disciples include David Starr Jordan, who was hugely impactful in creating a eugenics movement in the US and Europe. He wanted to eliminate the ‘unfit’ like the poor, handicapped, alcoholics, etc. Read more about Jordan in Lulu Miller’s Why Fish Don’t Exist.¹² Jordan’s academic tree includes almost every ichthyologist in the US including me, but we only inherited his love of taxonomy and fish, and the racists traits were lost (I hope). The modern creationist movement is motivated by a different religious perspective than differences in science philosophy but that may have been true of Agassiz’s motivations as well.¹³

* I know what you are thinking—why not just say ‘closest relatives’ then, instead of adding unnecessary technical language. Well, usually I try to avoid jargon, but in this case I want you to do a little ‘tree thinking’ (I know more jargon) and see the Tree of Life in your mind and think of closest relatives being equals, like twins from a mother. I think it helps explain the uncertainty built into looking for ancestors and shows how we leave room for the discoveries of new relationships in the present and the past. Such is the beauty of studying the Tree of Life—the uncertainty is built in and upfront.

** Again, see Neil Shubin’s Your Inner Fish⁶—I wish I could write a book called Your Inside Fish’ that was a cheap knock off. In fact, I was asked once to do essentially that, but wrote this book instead.

* I really like Olsansky et al.’s 2001 ‘If humans were built to last’¹ depiction of how to build a better human. It ain’t pretty though. Not as pretty as a teleost anyway.

** Bill Bryson writes that ‘we were built to choke’.¹¹ We have longer necks than other primates probably as a function of our bipedalism, which may have also endowed us with the ability to speak, which also gave us the ability to choke—it’s all a circular mess.⁹

* My TED talk on evolution covers the ‘you are a fish’ subject fairly well I’d say: ‘Four Billion Years of Evolution in Six Minutes’.⁵

* If you want to get into the real details of the logic and philosophy of science and evolution read, Elliott Sober’s Evidence and Evolution: The Logic Behind the Science.³

** If you just read Sober’s book in the last few lines, turn back to page 130 of that text. I like Karl Popper’s philosophy (I could sense the philosophers sucking their teeth) of ‘falsification’. Set up hypotheses and try to prove them false, and if you can’t, that doesn’t make them true, just not ‘untrue’. Keep testing them in different ways. If you still can’t prove the hypothesis false, they stand the test of time, but you must continue to test these hypotheses rigorously. Anyway, read more Sober—he’s very smart, interesting and ‘sobering’. Another way of seeing the importance of Popper’s philosophy is David Deutsch’s TED talk ‘A New Way to Explain Explanation’.

*** What is life? It is whatever separates the inanimate from the animate. It is this ancient question that Aristotle struggled with in De Anima. How do you know something is alive? Do you know you are alive? Cogito ergo sum. Maybe the distinction between the ‘living’ and ‘non-living’ is indefinable and irrelevant, maybe our real legacy as clumps of matter is how we transform energy. Maybe that’s all we are: weak signatures of transforming bundles of evolving energy floating in finite periods of time and pools of space until the inevitable heat death of the universe comes to erase us all. (You see why I made this a footnote?!?) While we are at it, what is death? When you ‘die’, not all of your cells die all at once, and many of the cells that make you you, are actually your bacterial symbionts. So when do you actually die? When all the cells with your DNA die? But what about the DNA you passed down to your children, or the DNA your family passed down that you share with them? But I digress; let’s stick to defining life, which I do later in this section.

* Check out the amazing talk by Sarah Hird explaining why humans are just a convenient transportation device for the many microbes that control us. This may be the greatest talk of all time. https://www.youtube.com/watch?v=6jGDPH5h_Mg

** I say that mostly to annoy my mammologist friends, but the average person thinks mammals are way more diverse than they are—it’s not all platypus and pandas, kids; 75% of mammal species are rodents or bats.²¹

* If you want to get an idea of how far we are going with CRISPR already, check out Unnatural Selection, a documentary series on Netflix, or Walter Isaacson’s book, The Code Breaker.

** For many, not only those in the deaf community, deafness is not an ‘illness’ that needs to be cured. Are we going to ‘cure’ Down syndrome into extinction? Autism? For some, that’s a call for the extinction of communities. For a look at the historical context for the use of CRISPR-Cas on humans, see Carl Zimmer’s excellent She Has Her Mother’s Laugh.¹⁹

*** For an even more shocking look at how humans are becoming the real ‘intelligent designers’ of nature, read Yuval Harari’s Homo Deus. It is from that book that I learned to repurpose that old creationist phrase for what we are doing to manipulate life on Earth.²¹

* I am a former programme director at the US National Science Foundation, one of the world’s greatest funders of basic science research. I loved that institution’s foundational charter—Vannevar Bush’s ‘Science, the Endless Frontier’,1 which laid out the importance of basic science. People used to call this fundamental basic research ‘true science’, and it was seen to be in poor taste to do any applied ‘money-earning’ research as a scientist. That elitism kept Thomas Edison out of the US National Academy of Science for some time, and why neither he or Nikola Tesla ever won the Nobel Prize.² That view has flipped—the trend now is to look at natural history and other ‘basic science’ as cheap and ‘basic’, with much of the funding and attention going to the ‘applied’ sciences like medicine or bioengineering.

** If you don’t think taxonomy matters, tell me the difference between ‘coronavirus’, ‘COVID-19’ and ‘SARS-CoV-2’. The differences are between a class of organisms, the disease it causes and the actual virus name. It may seem subtle, but it helps scientists be precise in order to keep track of the information related to these vastly different subjects.

* Check out the excellent blog of evolutionary geneticist Graham Coop: https://gcbias.org/. He understands the strange and odd dynamics of DNA heredity in humans better than anyone I know. It’s annoying that I can’t understand half of what he does.

** In reality. this ‘2%’ is only from the 1% or so of total variable DNA that most testing agencies actually examine. You can be ‘100% French’ and ‘2% Neanderthal’. When you get these DNA tests, they are ‘genotyping’, looking at specific variable regions of your genome. But we often say ‘get your genome sequenced’ as a shorthand for ‘genotyping’. Perhaps we should stop. Check out my TED-Ed video ‘What can DNA tests really tell us about our ancestry?’¹¹

*** I can’t recommend Angela Saini’s recent book Superior enough.²² It is a very scientific but very readable take on racism in science and culture. Speaking of equality in science, I have to call out my own colleagues in evolutionary biology, of whom only a very small fraction are Black, and that paucity can best be explained by systematic racism in our academic fields.²⁷–²⁹ We academics also need to be more inclusive towards indigenous communities, who we have failed, over and over, particularly with respect to genetics/genomic research.³⁰

*** Yes I capitalize ‘Black’ and not ‘white’ when referring to Black as an ethnicity. White is not considered an ethnicity, just a skin colour of many ethnicities. See also the latest AP Stylebook.³⁶

* There are lots of examples of intersex, and sex-fluid animals in Joan Roughgarden’s Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People.⁶

** Learn more about Jeremy from his website https://jbyoder.org/

*** See what I did there? I almost threw in ‘philallatopism’, which is the pleasure of revealing the ignorance of others. Anyway, Edith Hall brilliantly explains Aristotle’s way in her book Aristotle’s Way.26 He wasn’t a ‘philallatopist’, in fact he spent a lot of time on ‘exoteric’ work translating his ‘esoteric’ scientific work to the general public. Sounds like science communication to me. He also was very open to changing his mind about something when provided new evidence or a reasonable argument; that’s really Aristotle’s way: keeping an open mind.²⁶

* Joe whips out his smart phone. Pro shows him how to look up papers on GoogleScholar.com by typing in ‘human evolution’, ‘natural selection’ etc. He teaches him to compare scientific articles with methods and results from opinion pieces or fake news and commentaries. Pro buys Joe a beer and gives him a card to tell him to reach out if he has more questions or if he can’t get access to a paper. Pro tells Joe to look up the journals Evolution, Systematic Biology and Science for more about the topic. He then gives him a discount code for Explaining Life Through Evolution, a new book he wrote that he hopes can help explain the basics of evolution to anyone who is interested.

* Funny to me that he mentions Darwin for economics instead of Adam Smith, whose eighteenth-century free market, winner-take-all approach is a forerunner to natural selection.

** If you want a dark history of one of the deadliest virus pandemics ever, the so-called ‘Spanish’ flu (so-called because it definitely didn’t start in Spain; the US Mid-West is a more likely origin), read Laura Spinney’s chilling and academic Pale Rider.⁸

*** I thought Sonia Shah does an excellent job in her book Pandemic⁹ explaining the psychology behind people resisting germ theory.

**** As pointed out by the great Carl Zimmer,¹⁰ to the chagrin of the president.

Glossary

Allele—a version of a gene, often expressed as dominant or recessive in simplified form, such as in an allele for purple flowers versus the allele for yellow flowers, where the dominant purple allele can mask the recessive yellow allele.

Allopatric speciation—the formation of new species (speciation) after a novel barrier splits a population; in this case isolation causes speciation in the geographically separated populations.

Anthropocene—the current geological epoch is called the ‘Holocene’, but some prefer to call the period of time since humans began destructively manipulating the planet the ‘Anthropocene’. This term is in recognition of extinctions, the replacement of wildlife with livestock and the general transformation of the landscape and seascape by humans that some see akin to other seismic geological/biological shifts that defined epochs in the Earth’s past.

Archaea—a domain of life (one of three, with bacteria and eukaryotes) that are mostly extremophile, superficially ‘bacteria-like’ creatures, sometimes lumped in with bacteria as ‘prokaryotes’ (to differentiate them from the mostly multi-cellular eukaryotes).

Artificial selection—when humans co-opt the law of natural selection by being the force that chooses or manipulates the breeders (and survivors) among domesticated animals in order to select for particular preferred traits. We used artificial selection to get our various dog breeds, to get cows to produce prodigious amounts of milk and to get corn that grows much bigger than its wild ancestors. Artificial selection now includes direct manipulation of the genotype to obtain traits we prefer (like the non-browning Arctic Apple¹).

Catastrophism—the idea that big sudden cataclysmic events led to major changes in the history of the Earth. These events could be an asteroid striking the planet, earthquakes or other incidents. Early on, catastrophism was seen to be in opposition of Darwin’s slow and gradual change (i.e., uniformitarianism). Catastrophism was also the predominant geological world-view for ‘young-Earth’ proponents before uniformitarianism explained how slow and gradual geological processes were the norm and pointed to a very, very old Earth (see the works of James Hutton² and Darwin’s friend Charles Lyell³).

Coding regions—the part of a gene that is read to create a protein; a ‘non-coding region’ is sometimes termed ‘junk DNA’ because a mutation in these areas may have little consequence, while changes within the reading frame (i.e., the coding region) can be disastrous.

Creationist—someone who believes a non-evolutionary (sometimes anti-science) religious view of human origins or of all life on Earth. They come in many flavours, including Biblical literalists that believe a man, ‘Adam’, was created first and named all the animals on Earth (he was a taxonomist! the real oldest profession!) and then a woman, ‘Eve’, was created from Adam’s rib.4,5 Not all Christian creationists believe this literal view, and there are many deeply religious people who have no problem fitting the narrative of their religion with a belief system that also accepts science.5,6

CRISPR—shorthand for ‘clustered regularly interspaced short palindromic repeats’, an immune mechanism by which bacteria and archaea fight off viruses by cutting out the virus’s introduced DNA and replacing it with a benign sequence that works ‘to remember’ in case that virus attacks again; it has been co-opted by scientists as a genetic editing tool (known fully as CRISPR-Cas) that can be thought of as a ‘typewriter’ for changing DNA sequences.

Epigenetics—the study of how the environment influences the phenotype without heritable changes in the DNA sequence. Epigenetics explains why identical twins aren’t exactly the same or why a smoker may have some genes shut off because of DNA damage; these differences aren’t coded into the DNA but rather involve how the DNA is read.

Eukaryotes—all multicellular life (and a handful of unicellular forms) are eukaryotes, including plants, fungi and animals—pretty much everything but bacteria and archaea. Unlike those other groups, eukaryotes have cells with a nucleus containing DNA arranged in chromosomes (the other groups typically have a single circular chromosome and no nucleus).

Evolution—the process by which species are born, formed and modified leading to all known life. (For the purposes of this book, we are using the definition of ‘Organic Evolution’; not the ‘evolution’ of other things such as boy bands.) See also the more detailed definitions of ‘evolution’ that I’ve sprinkled throughout this book.

Gene drives—a genetic mechanism that can ‘fix’ any gene variant (allele) by ensuring that it is spread to all individuals in a population. As it has been co-opted by geneticists, that means you can make a trait like ‘HIV-resistance’ pass down 100% of the time to the offspring of a human who has this trait plus the gene-drive transmission mechanism. The gene drive helps break the rules of Mendelian inheritance. We haven’t used gene drives in humans yet because we don’t know what would happen if that transmission mechanism jumped to another species via a virus or some other mechanism or jump to other non-target traits, making us not just disease resistant but also tall and handsome. Gene drives have enormous potential, but their implementation requires an abundance of caution.

Genetic drift—the process by which populations/species diverge by non-adaptive changes (including changes in frequencies of different alleles) in their DNA sequences, including accumulating different neutral mutations. Genetic drift is perhaps the most significant contributor of genetic change/evolution of any natural process.

Genome—the totality of DNA from an organism, usually referring to the DNA in the nucleus arranged in chromosomes; the ‘mitogenome’ is all the DNA in the mitochondria of an organism.

Genotype—anything in reference to the totality of DNA of an organism; as opposed to the ‘phenotype’ as a physical or behavioural representation based on that genotype. The genotype includes the genes, genetic architecture and genome (i.e., the full suite of DNA).

Genotyping—the process by which someone’s DNA is examined for a few thousand commonly variable markers of the human genome (far less than even 1% of the total genome is examined). Sometimes people say they had their ‘genome sequenced’ when really they were genotyped, which is usually plenty for genealogy tests. Your DNA can actually vary (because of mutations) anywhere in your genome compared to another human, but the markers examined in genotyping are used as a short-cut for helping us understand how your DNA generally compares to reference (fully sequenced) genomes.

Homologous—heritable traits in different organisms (no matter the function) that are derived from the same common ancestor. Therefore, we say the fin of a coelacanth, which has the same pattern of limb bones that we humans have, and that of a dolphin’s fin, or a bird’s wing—are all homologous, i.e., they are all derived from the same common vertebrate ancestor that first evolved those limb bones. The wings of a fly and the wings of a bird are considered ‘analogous’ (i.e., not homologous) because you can’t trace the origins of their wings to the same ancestor, because the wings in these groups evolved independently.

Hypothesis—An answer to a question that explains some natural phenomena: e.g., ‘apples fall to the ground when dropped because of gravity’; or ‘apples fall to the ground when dropped because wind pushes it to the ground’. Note that both are hypotheses; science is about testing competing answers to see which is the best explanation for the phenomenon. We continually return to these hypotheses and refine them based on the results of additional testing and as new information and new technologies arise.

Macroevolution—large-scale evolution over deep time; the sum of microevolutionary processes. Examples are the origin of whales or of flowering plants.

Meiosis—the formation of sex cells (e.g., eggs and sperm); in humans, who have two sets of chromosomes, the sperm or egg gets a unique mix represented in a single chromosome set. During meiosis, a single cell divides twice to make four daughter cells (each with half the chromosome number as the parent cell). The daughter cells (egg and sperm) that combine during reproduction again have two sets of chromosomes formed from that union.

Microevolution—‘small-scale’ evolution such as genetic drift or natural selection acting on populations, typically taking place over relatively short periods of time (e.g., generational scale, not a geological time scale).

Mutations—at the level of the genotype, a mutation is any change in your DNA sequence that you did not inherit.

Natural group—a group of organisms that includes the ancestor and all its descendants is considered a ‘natural group’ or ‘monophyletic’; such as ‘birds’ when it is represented by Archaeopteryx and all other birds living and extinct. However, because birds are a lineage of dinosaurs, you couldn’t talk about ‘dinosaurs’ as a natural group unless you also included birds. Monophyletic groups are real units of evolution because of their shared history, as opposed to say ‘bugs’ in the colloquial sense, which may include everything from insects (like the Hemiptera or ‘true bugs’) and ‘pill bugs’ (which are actually crustaceans) and other small creepy-crawlies that are distantly related and don’t share common ancestry.

Natural selection—the process by which individuals compete to survive in an environment; those that are best fit will survive to produce the next generation. Natural selection was ‘co-discovered’ by Charles Darwin and Alfred Russel Wallace, but it was made famous and described more thoroughly by the former in the Origin of Species.

Neutral evolution—also ‘neutral theory of molecular evolution’ championed by Mootoo Kimura; it is the hypothesis that most genetic mutations do nothing to the phenotype; therefore, most evolutionary change is neutral.

Phenotype—the outward expression of the genotype, including everything from the proteins created by DNA to the body and behaviour of the organism.

Phylogenetics—the study of relationships on the Tree of Life, which is an evolutionary depiction of the relationships of all life on Earth.

Point mutations—a single change (mutation) in a DNA sequence, including changes from an ‘A’ to a ‘C’ or a deletion or insertion of any DNA base (viz., A, C, T, G).

Polymorphisms—natural states of variation for a given trait in a population, for instance blond, black, brown or red hair.

Polyploidy—the formation of more than the typical number of sets of chromosomes for an individual or species. Having a genome duplication event can result in polyploidy. This process can cause speciation or evolutionary innovations. After duplication, you may end up with duplicate sets of genes that do identical tasks, so one set can be freed up to evolve to do something else.

Recombination—the act of mixing the DNA from separate sets of chromosomes for daughter cells, which will each get half the original number of chromosomes. In the formation of sex cells (during meiosis) like sperm and eggs, a parent with two sets of chromosomes creates these sex cells by recombining the two chromosome sets into a single set. Recombination is both a major source of variation and of loss of variation in sexually reproducing organisms.

Sexual selection—not a Snoop Dogg song but rather a theory introduced by Charles Darwin in the Origin of Species that explains why some animals have individual sexes (usually males in vertebrates) with conspicuous traits (like bright colours or a loud call) that might threaten their survival (by being more susceptible to predation) but that also makes them more attractive to potential mates.

Sister groups—a pair of closest relatives on the Tree of Life, these ‘sister pairs’ are how we depict the relationships of organisms on the bifurcating tree. Why not just say closest relatives? Because the true closest relatives of either of the descendants would be that shared ancestor, and we don’t know the exact ancestor (those ‘nodes’ remain unnamed on the tree). Therefore, by saying ‘sister groups’, we are acknowledging that uncertainty and recognizing the limits by which we can reconstruct the past.

Speciation—the evolutionary processes by which new species arise from an ancestor.

Species—population(s) of interbreeding or potentially interbreeding individuals, or a distinct evolutionary lineage with some heritable features that make them distinct from other such lineages. What a species is exactly remains a hotly debated topic—look up ‘Evolutionary Species Concept’, ‘Phylogenetic Species Concept’ or ‘Biological Species Concept’, among dozens more. The reason behind the concept is to help shape evolutionary thought as species are the product of evolution; but there is no one-size-fits-all definition that works across the diversity of life.

Sympatric speciation—the formation of new species without any physical geographic barriers; isolation in sympatric speciation can be caused by factors such as pre-mating assortment (e.g., females attracted to particular types of males) or post-mating factors (e.g., certain male’s genes not contributing to the next generation); or mechanisms like polyploidy may also explain speciation in the absence of physical barriers.

Taxonomist—someone who works on the naming and describing of new species or lineages; they also organize the biodiversity of life within a hierarchy of names.

Theory—an overarching explanation for some natural phenomena, not ‘a tenuous idea’, as it is used in non-scientific language; more similar to what most people think of as a ‘law’ in the scientific parlance. However, like hypotheses, theories are also continually refined and examined by scientific testing.

Tree of Life—the depiction of the relationships of life on Earth as a series of (usually bifurcating) ancestor–descendant relationships. Put more simply, it is an evolutionary diagram showing which species are related to what other species.

Uniformitarianism—slow and gradual change of organisms or geological formations can lead to big differences over time (i.e., continental drift across oceans). The continents move at the speed your fingernails grow but over 100 million (100,000,000) years that can add up to thousands of miles. Similarly, a population of tortoises that was split into two by the formation of a barrier (like a lava flow) or by some members dispersing onto a new island can accumulate enough changes over thousands of years to become different species. (See also ‘catastrophism’.)

Viruses—are they life, or are they not? Depends on how you define ‘life’. Most scientists see them as peripheral to the three branches of life we all agree upon (viz., eukaryotes, bacteria, archaea) because they need other organisms to make copies of themselves and don’t eat sandwiches. Think of viruses like a parasitic vine that grows on the Tree of Life. That vine interjects its genetic code along many of the branches of the tree and even moves some of the host branch’s code around to different parts of the tree, but the vine (i.e., the viruses) cannot replicate on its own.

Vouchers—in the context of this book and biological research, vouchers are preserved specimens stored (usually) in museum collections. Vouchers can be used to verify the identification of a species used in a study. They can also be used in various kinds of studies, including providing evidence of shifting levels of pollution or to document extinctions.

References/Further Reading

Citation Diversity Statement—Zurn et al. 2020¹ suggest that authors include ‘Citation Diversity Statements’ such as this one to combat the negative biases that result in under-citing women and people from other groups underrepresented in the sciences. In an attempt to make science more equitable, I’ve tried to have references that reflect the diversity of the field of evolutionary biologists and others in the life sciences. Unfortunately, I’m sure I’ve missed some important references, despite my best efforts; apologies in advance.

1. Zurn, P., Bassett, D.S., and Rust, N.C., 2020. The citation diversity statement: A practice of transparency, a way of life. Trends in Cognitive Sciences 24(9), pp.669–672.

Introduction to Indian Edition

1. Dash, B., and Junius, A.M.M., 1997. Handbook of Ayurveda. Concept Publishing Company.

2. Marshall, J., 2015. ‘The evolution of the word “evolution”.’ OUPblog (May 9, 2015). https://blog.oup.com/2015/05/word-evolution-etymology/.

PART I. A Personal Prologue

Called to Action

1. Mead, L.S., and Mates, A., 2009. ‘Why Science Standards are Important to a Strong Science Curriculum and How States Measure Up’. Evolution: Education and Outreach 2: 359–371.

https://evolution—outreach.biomedcentral.com/articles/10.1007/s12052-009-0155-y.

2. Rayfield, J., 2013. ‘Bobby Jindal: I’m fine with teaching creationism in public schools’. Salon. https://www.salon.com/2013/04/16/bobby_jindal_im_fine_with_teaching_creationism_in_public_schools/.

3. ‘Birth of the World—a Hindu Creation Myth’. Haidakhandi International Journal. https://hi-journal.com/index.php/misc/death-and-birth-the-cycle-of-life/birth-of-the-world-a-hindu-creation-myth/.

4. Thiagarajan, K., 2019. ‘Indian Science Congress Speakers Say Newton Was Wrong, Ancient Demon-King Had Planes’. National Public Radio. https://www.npr.org/sections/goatsandsoda/2019/01/09/683298815/speakers-at-indian-science-congress-say-newton-was-wrong-ancient-demon-had-airpl?fbclid=IwAR25Vpm1JLVm4sYEx4kZOtypJXYz8pQ0pZ0oz1PqXnfeRB6tuFH6SGX65M8&fbclid=IwAR0jetg5KauDIFwmIuj5
YtlormY0XgZ5EnOS0km7X_WGPlp8hPMVgM7lYzY.

5. Gould, S.J., 2002. Rocks of Ages: Science and Religion in the Fullness of Life. New York: Ballantine Books.

6. Barnes, M.E., and Brownell, S.E., 2017. ‘A call to use cultural competence when teaching evolution to religious college students: Introducing Religious Cultural Competence in Evolution Education (ReCCEE)’. CBE—Life Sciences Education 16(4): 4.

7. Branch, G., 2016. ‘Alabama retains its evolution disclaimer’. National Center for Science Education. https://ncse.ngo/news/2016/03/alabama-retains-its-evolution-disclaimer-0016968.

8. Timmer, J., 2018. ‘Arizona state education standards see evolution deleted: Never mention “change over time” by its name’. ARS Technica. https://arstechnica.com/science/2018/05/arizona-official-waters-down-states-science-education-standards/.

9. Plutzer, E., Branch, G., and Reid, A., 2020. ‘Teaching evolution in U.S. public schools: a continuing challenge’. Evo Edu Outreach 13, 14. https://doi.org/10.1186/s12052-020-00126-8.

10. Bell, J., Lugo, L., Cooperman, A., Sahgal, N., Martinez, J.H., Mohamed, B., Robbins, M., Simmons, K., Kuriakose, N., Sciupac, E.P., Ghani, F., et al., 2013. The World’s Muslims: Religion, Politics and Society, Chapter 7: Religion, Science and Popular Culture. Pew Research Center. http://www.pewforum.org/2013/04/30/the-worlds-muslims-religion-politics-society-science-and-popular-culture/.

11. Kingsley, P., 2017. ‘Turkey Drops Evolution from Curriculum, Angering Secularists’. The New York Times. https://www.nytimes.com/2017/06/23/world/europe/turkey-evolution-high-school-curriculum.html.

12. Le Page, M., 2008. ‘Evolution myths: It doesn’t matter if people don’t grasp evolution’. New Scientist 198(2652): 31, doi:10.1016/S0262-4079(08)60984-7

13. Bast, F., and Tahilramani, H., 2018. ‘Public Acceptance of Evolution in India’. Journal of Scientific Temper (JST) 6(1–2).

14. Jogelekar, A., 2013. ‘Monday morning levity: Louisiana senator asks if E. coli evolve into persons’. Scientific American.

15. Blount, Z.D., Lenski, R.E., and Losos, J.B., 2018. ‘Contingency and determinism in evolution: Replaying life’s tape’. Science 362: 655 (review summary) and Science 362: eaam5979 (full review article).

16. Lenski, R.E., 2020. The E. coli long-term experimental evolution project site. http://myxo.css.msu.edu/ecoli.

17. Losos, J.B., 2017. Improbable Destinies: Fate, Chance, and the Future of Evolution. Penguin.

Pulled into the Fight

1. Forrest, B., and Gross, P.R., 2004. Creationism’s Trojan Horse: The Wedge of Intelligent Design. Oxford University Press. https://doi.org/10.1093/acprof:oso/9780195157420.001.0001.

2. Heist, A., 2013. ‘The teenage “troublemaker” fighting for science’. Science Friday. https://www.sciencefriday.com/segments/the-teenage-troublemaker-fighting-for-science/.

3. Zeberg, H., and Pääbo, S., 2020. ‘The major genetic risk factor for severe COVID-19 is inherited from Neanderthals’. Nature. https://doi.org/10.1038/s41586-020-2818-3.

4. Scott, E.C., 2008. Evolution vs. Creationism: An Introduction. ABC-CLIO.

On Trust

1. Barnes, M.E., and Brownell, S.E., 2017. ‘A call to use cultural competence when teaching evolution to religious college students: Introducing Religious Cultural Competence in Evolution Education (ReCCEE)’. CBE—Life Sciences Education 16(4): 4.

2. Rissler, L.J., Duncan, S.I., and Caruso, N.M., 2014. ‘The relative importance of religion and education on university students’ views of evolution in the Deep South and state science standards across the United States’. Evolution: Education and Outreach 7(1): 24. https://doi.org/10.1186/s12052-014-0024-1.

Facts and Truth

1. Allcott, H., and Gentzkow, M., 2017. ‘Social media and fake news in the 2016 election’. Journal of Economic Perspectives 31(2): 211–36.

2. Nielsen, J., Hedeholm, R.B., Heinemeier, J., Bushnell, P.G., Christiansen, J.S., Olsen, J., Ramsey, C.B., Brill, R.W., Simon, M., Steffensen, K.F. and Steffensen, J.F., 2016. ‘Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)’. Science 353 (6300): 702–704.

3. Van Kranendonk, M.J., Philippot, P., Lepot, K., Bodorkos, S., and Pirajno, F., 2008. ‘Geological setting of Earth’s oldest fossils in the c. 3.5 Ga Dresser Formation, Pilbara craton, Western Australia’. Precambr. Res. 167: 93–124.

4. Einstein, A. 1905. ‘Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig?’ Annalen der Physik 18(13): 639–643, doi:10.1002/andp.19053231314.

5. Wolfson, S. 2019. ‘“Germs are not a real thing”: Fox News host says he hasn’t washed hands in 10 years’. The Guardian. https://www.theguardian.com/media/2019/feb/11/germs-are-not-real-fox-news-host-pete-hegseth.

6. Gohd, C. 2019. ‘“Mad” flat-earther to launch himself 5,000 feet up on a homemade steam rocket Sunday’. Space.com. https://www.space.com/flat-earther-mad-mike-hughes-august-2019-launch.html.

PART II: The Evolution Revolution

Introduction to Evolution

1. Clack, J., 2006. ‘The emergence of early tetrapods’. Palaeogeography, Palaeoclimatology, Palaeoecology 232(2–4): 167–189. https://www.sciencedirect.com/science/article/abs/pii/S003101820500444X?via%3Dihub.

2. Carroll, R.L., 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Co.

3. Gilbert, M.M., Snively, E., and Cotton, J., 2016. ‘The tarsometatarsus of the Ostrich Struthio camelus: Anatomy, bone densities, and structural mechanics’. PloS one 11(3).

4. Qiu, T.X., Teo, E.C., Yan, Y.B., and Lei, W., 2011. ‘Finite element modeling of a 3D coupled foot–boot model’. Medical Engineering & Physics 33(10): 1228–1233.

5. Gould, S.J. 1980. The Panda’s Thumb: More Reflections in Natural History. W.W. Norton & Company.

6. Shubin, N., 2008. Your Inner Fish. Pantheon.

7. Diogo, R., and Ziermann, J.M., 2014. ‘Muscles of chondrichthyan paired appendages: Comparison with osteichthyans, deconstruction of the fore–hindlimb serial homology dogma, and new insights on the evolution of the vertebrate neck. The Anatomical Record 298(3): 513–530. https://doi.org/10.1002/ar.23047.

8. Pradel, A., Maisey, J., Tafforeau, P. et al., 2014. ‘A Palaeozoic shark with osteichthyan-like branchial arches’. Nature 509: 608–611. https://doi.org/10.1038/nature13195.

9. Brazeau, M.D., Giles, S., Dearden, R.P. et al., 2020. ‘Endochondral bone in an Early Devonian “placoderm” from Mongolia’. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01290-2.

10. Bernal, D., Sepulveda, C., Mathieu-Costello, O., and Graham, J.B., 2003. ‘Comparative studies of high performance swimming in sharks I. Red muscle morphometrics, vascularization and ultrastructure’. Journal of Experimental Biology 206(16): 2831–2843.

11. Chen, F.-C., and Li, W.-H., 2001. ‘Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees’. The American Journal of Human Genetics 68 (2): 444–456, doi:10.1086/318206.

12. Paixão-Côrtes, V.R., Viscardi, L.H., Salzano, F.M., Hünemeier, T., and Bortolini, M.C., 2012. ‘Homo sapiens, Homo neanderthalensis and the Denisova specimen: new insights on their evolutionary histories using whole-genome comparisons’. Genetics and Molecular Biology 35(4 suppl 1): 904–911, doi:10.1590/s1415-47572012000600003.

13. Banks, W.E., d’Errico, F., Peterson, A.T., Kageyama, M., Sima, A., and Sánchez-Goñi, M.F., 2008. ‘Neanderthal extinction by competitive exclusion’. PLoS ONE 3(12).

14. Quammen, D., 2007. The Reluctant Mr. Darwin: An Intimate Portrait of Charles Darwin and the Making of His Theory of Evolution (Great Discoveries). W.W. Norton & Company.

15. Hug, L., Baker, B., Anantharaman, K. et al., 2016. ‘A new view of the tree of life’. Nature Microbiology 1(16048). https://doi.org/10.1038/nmicrobiol.2016.48.

The Great Chain of Being/Ladder of Life

1. Ragan, M., 2009. ‘Trees and networks before and after Darwin’. Biology Direct 4: 43.

2. Pietsch, T.W., 2012. Trees of Life: A Visual History of Evolution. Johns Hopkins University Press, 376.

3. Peterson, J.B., 2018. 12 Rules for Life: An Antidote to Chaos. Penguin Random House.

4. Myers, P.Z., 2018. ‘PZ Replies to the Lobsterians’. Youtube.com. https://www.youtube.com/watch?v=Sqx57l781WM.

5. Ramenofsky, M., 2010. ‘Behavioral endocrinology of migration’. In: Encyclopedia of Animal Behavior, ed. Michael D. Breed and Janice Moore. Academic Press, pp. 191–199. https://doi.org/10.1016/B978-0-08-045337-8.00252-7.

6. Monk, J.D., Giglio, E., Kamath, A., Lambert, M.R., and McDonough, C.E., 2019. ‘An alternative hypothesis for the evolution of same-sex sexual behaviour in animals’. Nature Ecology & Evolution 3(12): 1622–1631.

7. Long, J.A., 2012. Dawn of the Deed: The Prehistoric Origins of Sex. University of Chicago Press.

8. Aubert-Marson, D., 2009. ‘Sir Francis Galton: The father of eugenics’. Medicine sciences 25(6–7): 641–645, doi: 10.1051/medsci/2009256—7641.

Theories of Evolution

1. Darwin, C., 1859. On the Origin of Species by Means of Natural Selection, or Preservation of Favoured Races in the Struggle for Life. John Murray.

2. Mayr, E., 2001. What Evolution Is. Basic Books.

3. Darwin, C., 1896. The Descent of Man and Selection in Relation to Sex. D. Appleton.

4. Kimura, M., 1983. The Neutral Theory of Molecular Evolution. Cambridge.

5. Paul, D.B., 1988. ‘The selection of the “Survival of the Fittest”’. Journal of the History of Biology 21: 411–424, https://doi.org/10.1007/BF00144089.

6. Paul, D.B., 2003. ‘Darwin, social Darwinism and eugenics’. The Cambridge Companion to Darwin. Cambridge University Press, 214.

7. Dennis, R.M., 1995. ‘Social Darwinism, scientific racism, and the metaphysics of race’. Journal of Negro Education: 243–252.

8. Prum, R.O., 2017. The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World-and Us. Anchor.

From So Simple a Beginning

1. Darwin, C., 1993. The Autobiography of Charles Darwin, 1809–1882: With original omissions restored. W.W. Norton & Company.

2. Quammen, D., 2007. The Reluctant Mr. Darwin: An Intimate Portrait of Charles Darwin and the Making of His Theory of Evolution (Great Discoveries). W.W. Norton & Company.

3. Browne, E.J., 2010. Charles Darwin: Voyaging: Volume 1 of a Biography. Random House.

4. Browne, E.J., 2003. Charles Darwin: The Power of Place (Vol. 2). Princeton University Press.

POSTSCRIPT:

5. Freeman, R.B., 1978. ‘Darwin’s negro bird-stuffer’. Notes and Records of the Royal Society of London 33: 83–86.

The Selection of Natural Selection

1. Darwin, C., 1859. On the Origin of Species by Means of Natural Selection, or Preservation of Favoured Races in the Struggle for Life. John Murray.

2. Lurie, E., 1954. ‘Louis Agassiz and the Races of Man’. Isis 45(3): 227–242.

3. Lamarck, Jean Baptiste Pierre Antoine de Monet, 1873. Philosophie zoologique, ou exposition des considérations relatives à l’histoire naturelle des animaux. F. Savy.

4. Weismann, A., 1891. Essays upon Heredity and Kindred Biological Problems. Oxford: Clarendon Press, 1.

5. Sobo, E.J., 2016. ‘What is herd immunity, and how does it relate to pediatric vaccination uptake? US parent perspectives’. Social Science & Medicine 165: 187–195. doi:10.1016/j.socscimed.2016.06.015.

6. Chambers, R., 1844. Vestiges of the Natural History of Creation. John Churchill.

7. Wallace, A.R., 1869. The Malay Archipelago. Harper.

8. Raby, P., 2002. Alfred Russel Wallace: A Life. Princeton University Press.

9. Gleick, J., 2004. Isaac Newton. Random House.

10. Frederick, S., 2013. Lost Enlightenment: Central Asia’s Golden Age from the Arab Conquest to Tamerlane. Princeton University Press.

11. Malik, A.H., Ziermann, J.M., and Diogo, R., 2018. ‘An untold story in biology: The historical continuity of evolutionary ideas of Muslim scholars from the 8th century to Darwin’s time’. Journal of Biological Education 52(1): 3–17.

12. Scott, R., 2012. Darwin’s Ghosts: The Secret History of Evolution. Bloomsbury Publishing.

13. Zimmer, C., 2018. She Has Her Mother’s Laugh. Penguin.

14. West-Eberhard, M.J., 2003. Developmental Plasticity and Evolution. Oxford University Press.

Mendel and the Maintenance of Variation

1. Galton, D., 2009. ‘Did Darwin read Mendel?’, QJM: An International Journal of Medicine 102: 587–589. https://doi.org/10.1093/qjmed/hcp024.

2. Vorzimmer, P., 1963. ‘Charles Darwin and blending inheritance’. Isis 54(3): 371–390, doi:10.1086/349734.

3. Deichmann U., 2010. ‘Gemmules and elements: On Darwin’s and Mendel’s concepts and methods in heredity’. In Darwinism, Philosophy, and Experimental Biology, ed. U. Deichman and A.S. Travis. Springer.

4. Kampourakis, K., 2013. ‘Mendel and the path to genetics: Portraying science as a social process’. Science & Education 22: 293–324. https://doi.org/10.1007/s11191-010-9323-2.

5. Fisher, R.A., 1936. ‘Has Mendel’s work been rediscovered?’, Annals of Science 1(2): 115–137, doi: 10.1080/00033793600200111.

6. Campbell, N., Cain, M., Wasserman, S., Minorsky, P., and Reece, P., 2017. Biology. 11th ed. Pearson.

7. Crow, J.F., 1994. ‘Advantages of sexual reproduction’. Genes and Development 15(3): 205–213, doi:10.1002/dvg.1020150303.

8. Olby, R., and Gautrey, P., 1968. ‘Eleven references to Mendel before 1900’, Annals of Science 24(1): 7–20, doi: 10.1080/00033796800200021.

9. Huxley, J., 1943. Evolution, the Modern Synthesis. Harper & Brothers.

10. Vecerek, O., 1965. ‘Johann Gregor Mendel as a beekeeper’. Bee World 46(3): 86–96, doi:10.1080/0005772x.1965.11095345.

Mutants and Mutations

1. Venter, J.C. et al., 2001. ‘The sequence of the human genome’. Science 291(5507): 1304–1351. https://science.sciencemag.org/content/291/5507/1304.

2. Kimura, M., 1968. ‘Evolutionary rate at the molecular level’. Nature 217(5129): 624–626.

3. Kimura, M., 1983. The Neutral Theory of Molecular Evolution. Cambridge.

4. Gusella, J., Wexler, N., Conneally, P. et al., 1983. ‘A polymorphic DNA marker genetically linked to Huntington’s disease’. Nature 306: 234–238, doi:10.1038/306234a0.

5. Stephen, W., 2010. ‘Genetic hitchhiking versus background selection: The controversy and its implications’. Philosophical Transactions of the Royal Society, B: Biological Sciences, 365(1544), pp.1245-1253. http://doi.org/10.1098/rstb.2009.0278.

6. Shiang, R., Thompson, L.M., Zhu, Y.Z., Church, D.M., Fielder, T.J., Bocian, M., Winokur, S.T., and Wasmuth, J.J., 1994. ‘Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia’. Cell 78: 335–342. https://doi.org/10.1016/0092—8674(94)90302—6.

7. Lindhurst, M.J., Sapp, J.C., Teer, J.K., Johnston, J.J., Finn, E.M., Peters, K. et al., 2011. ‘A mosaic activating mutation in AKT1 associated with the Proteus syndrome’. The New England Journal of Medicine 365(7): 611–619, doi: 10.1056/NEJMoa1104017.

8. Elena, I., Victor, L., Nikolay, Y., Mikhail, M., and Nikolay, K., 2014. ‘Genetic basis of olfactory cognition: Extremely high level of DNA sequence polymorphism in promoter regions of the human olfactory receptor genes revealed using the 1000 Genomes Project dataset’. Frontiers in Psychology 5: 247, doi: 10.3389/fpsyg.2014.00247.

9. Eriksson, N., Wu, S., Do, C.B. et al., 2012. ‘A genetic variant near olfactory receptor genes influences cilantro preference’. Flavour 1(22). https://doi.org/10.1186/2044-7248-1-22.

10. McClintock, B., 1950. ‘The origin and behavior of mutable loci in maize’. Proceedings of the National Academy of Sciences 36(6): 344–355, doi: 10.1073/pnas.36.6.344.

11. Sagan, L., 1967. ‘On the origin of mitosing cells’. Journal of Theoretical Biology 14: 225–274.

12. Quammen, D., 2018. The Tangled Tree: A Radical New History of Life. Simon & Schuster.

13. Cornelis, G., Funk, M., Vernochet, C., Leal, F., Tarazona, O.A., Meurice, G., Heidmann, O., Dupressoir, A., Miralles, A., Ramirez-Pinilla, M.P., and Heidmann, T., 2017. ‘An endogenous retroviral envelope syncytin and its cognate receptor identified in the viviparous placental Mabuya lizard’. Proceedings of the National Academy of Sciences 114(51): 10991–11000, doi: 10.1073/pnas.1714590114.

14. ‘Retroviruses turned egg-layers into live-bearers’. 2017. Virology blog: About Viruses and Viral Diseases. http://www.virology.ws/2017/12/14/a-retrovirus-gene-drove-emergence-of-the-placenta/.

15. Ryan, F.P., 2016. ‘Viral symbiosis and the holobiontic nature of the human genome’. APMIS 124(1–2): 11–19, doi:10.1111/apm.12488.

16. ‘Every Cell A Universe’. 2019. Virus DNA in human genome (evolution by infection). Youtube.com. https://www.youtube.com/watch?v=nWuV6PVKv1A. Many thanks to Jeet Sukumaran for spreading the word of this cool story to me.

17. NIH, National Institute of General Medical Sciences (NIGMS), 2016. ‘Our complicated relationship with viruses’. ScienceDaily. www.sciencedaily.com/releases/2016/11/
161128151050.htm.

18. Prachumwat, A., and Li, W.H., 2008. ‘Gene number expansion and contraction in vertebrate genomes with respect to invertebrate genomes’. Genome Research, 18(2): 221–232.

19. Margulis, L., and Fester, R., eds. 1991. Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis. MIT Press.

20. Guerrero, R., Margulis, L., and Berlanga, M., 2013. ‘Symbiogenesis: The holobiont as a unit of evolution’. International Microbiology 16(3): 133–143.

21. Yong, E., 2016. I Contain Multitudes: The Microbes Within Us and A Grander View of Life. Random House.

22. Moran, N.A., 1996. ‘Accelerated evolution and Muller’s rachet in endosymbiotic bacteria’. Proceedings of the National Academy of Sciences 93(7): 2873–2878.

23. Moran, N.A., 2007. ‘Symbiosis as an adaptive process and source of phenotypic complexity’. Proceedings of the National Academy of Sciences 104(suppl 1): 8627–8633.

24. McFall-Ngai, M., Hadfield, M.G., Bosch, T.C., Carey, H.V., Domazet-Lošo, T., Douglas, A.E., Dubilier, N., Eberl, G., Fukami, T., Gilbert, S.F., and Hentschel, U., 2013. ‘Animals in a bacterial world, a new imperative for the life sciences’. Proceedings of the National Academy of Sciences 110(9): 3229–3236.

25. Planck, M., 1950. Scientific Autobiography, and Other Papers with a Memorial Address on Max Planck by Max von Laue. Translated from German by Frank Gaynor. Williams & Norgate.

Speciation: The Formation of New Species

1. Otto, S.P., and Whitton J., 2000. ‘Polyploid incidence and evolution’. Annual Review in Genetics 34: 401–437.

2. Paun, O., Forest, F., Fay, M.F., and Chase, M.W., 2009. ‘Hybrid speciation in angiosperms: Parental divergence drives ploidy’. New Phytologist 182(2): 507–518.

3. Bergfeld, A.K., Lawrence, R., Diaz, S.L., Pearce, O.M.T., Ghaderi, D., Gagneux, P., Varki, A. et al., 2017. ‘N-glycolyl groups of nonhuman chondroitin sulfates survive in ancient fossils’. Proceedings of the National Academy of Sciences 114(39): E8155–E8164, doi:10.1073/pnas.1706306114.

4. Wilcox, C., 2020. ‘Extra DNA may make unlikely hybrid fish possible’. Quanta Magazine.

5. Káldy, J., Mozsár, A., Fazekas, G., Farkas, M., Fazekas, D.L., Fazekas, G.L., Goda, K., Gyöngy, Z., Kovács, B., Semmens, K., and Bercsényi, M., 2020. ‘Hybridization of Russian sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeberg, 1833) and American paddlefish (Polyodon spathula, Walbaum 1792) and evaluation of their progeny’. Genes 11(7): 753.

6. Chan, J.Z., Halachev, M.R., Loman, N.J. et al., 2012. ‘Defining bacterial species in the genomic era: Insights from the genus Acinetobacter’. BMC Microbiology 12: 302. https://doi.org/10.1186/1471-2180-12-302.

7. Darwin, C., 1889. Journal of Researches Into the Natural History and Geology of the Countries Visited During the Voyage of HMS’ Beagle’ Round the World, Under the Command of Capt. Fitz Roy. Ward, Lock and Company.

8. Weiner, J. 1994. The Beak of the Finch: A Story of Evolution in Our Time. Random House Inc.

On Fossils and the Book of Life

1. Owen, R., 1860. [Anonymous]. Darwin On the Origin of Species. Edinburgh Review 111(8): 487–532.

2. Darwin, C.R., 1861. On the Origin of Species by Means of Natural Selection, Or the Preservation of Favoured Races in the Struggle for Life. John Murray, 3.

3. Scott, R., 2012. Darwin’s Ghosts: In Search of the First Evolutionists. Bloomsbury.

4. Kidwell, S.M., and Flessa, K.W., 1995. ‘The quality of the fossil record: Populations, species, and communities’. Annual Review of Ecology and Systematics 26(1): 269–299. https://www.annualreviews.org/doi/abs/10.1146/annurev.es.26.110195.001413.

5. Baumgartner, R.J., Van Kranendonk, M.J., Wacey, D., Fiorentini, M.L., Saunders, M., Caruso, S., Pages, A., Homann, M., and Guagliardo, P., 2019. ‘Nano-porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life’. Geology 47(11): 1039–1043, doi: https://doi.org/10.1130/G46365.1.

6. Dodd, M.S., Papineau, D., Grenne, T., Slack, J.F., Rittner, M., Pirajno, F., O’Neil, J., and Little, C.T.S., 2017. ‘Evidence for early life in Earth’s oldest hydrothermal vent precipitates’. Nature 543(7643): 60–64, doi: 10.1038/nature21377.

7. Peters, S.E., 2008. ‘Environmental determinants of extinction selectivity in the fossil record’. Nature 454: 626–629. https://doi.org/10.1038/nature07032.

8. Alroy, J., 2002. ‘How many named species are valid’. Proceedings of the National Academy of Sciences 99(6): 3706–3711. https://doi.org/10.1073/pnas.062691099.

9. Williams, P., 2018. The Dinosaur Artist Obsession, Betrayal, and the Quest for Earth’s Ultimate Trophy. Hachette Books.

10. Appel, T., 1987. The Cuvier-Geoffroy Debate: French Biology in the Decades Before Darwin. Oxford University Press.

11. Lurie, E., 1959. ‘Victorian studies: Louis Agassiz and the idea of evolution’. Indiana University Press 3(1): 87–108. http://www.jstor.org/stable/3825589.

12. Miller, L., 2020. Why Fish Don’t Exist. Simon & Schuster.

13. Forrest, B., and Gross, P.R., 2004. Creationism’s Trojan Horse: The Wedge of Intelligent Design. Oxford University Press. https://doi.org/10.1093/acprof:oso/9780195157420.001.0001.

14. Brinkman, P.D., 2009. ‘Charles Darwin’s Beagle voyage, fossil vertebrate succession, and “The Gradual Birth & Death of Species’. The Journal of the History of Biology 43: 363–399. https://doi.org/10.1007/s10739-009-9189-9.

15. Darwin, C., 1839. Voyages of the Adventure and Beagle, Volume III. Journal and Remarks. Henry Colburn.

16. Lyell, C., 1830–1833. Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth’s Surface by Reference to Causes Now in Operation. John Murray, 3.

17. Gohau, G., 2010. ‘Darwin the geologist: Between Lyell and von Buch’. Comptes Rendus Biologies 333(2): 95–98. https://doi.org/10.1016/j.crvi.2009.11.008.

18. Wellnhofer, P., 2010. ‘A short history of research on Archaeopteryx and its relationship with dinosaurs’. Geological Society, London, Special Publications 343: 237–250. https://doi.org/10.1144/SP343.14.

19. Gingerich, P.D., 2003. ‘Land-to-sea transition in early whales: Evolution of Eocene Archaeoceti (Cetacea) in relation to skeletal proportions and locomotion of living semiaquatic mammals’. Paleobiology 29: 429–454, doi:10.1666/0094-8373(2003)029<0429:LTIEWE>2.0.CO;2.

20. Schneider, I., and Shubin, N.H., 2013. ‘The origin of the tetrapod limb: From expeditions to enhancers’. Trends in Genetics 29(7): 419–426. https://doi.org/10.1016/j.tig.2013.01.012.

21. Lyson, T.R., Bever, G.S., Bhullar, B.A.S., Joyce, W.G., and Gauthier, J.A., 2010. ‘Transitional fossils and the origin of turtles’. Paleontology 6: 830–833. https://doi.org/10.1098/rsbl.2010.0371.

22. String, C.B., and Andrews, P., 1988. ‘Genetic and fossil evidence for the origin of modern humans’. Science 239(4845): 1263–1268, doi: 10.1126/science.3125610.

PART III: Questions and Misconceptions

Who You Calling Primitive?

1. Tyndale-Biscoe, C.H., 2005. The Life of Marsupials. CSIRO Publishing.

2. Upham, N.S., Esselstyn, J.A., and Jetz, W., 2019. ‘Inferring the mammal tree: Species-level sets of phylogenies for questions in ecology, evolution, and conservation’. PLoS Biology 17(12): 3000494, doi:10.1371/journal.pbio.3000494.

3. Grant, T., 2007. Platypus, 4th edition. CSIRO Publishing.

4. Anich, P.S., Anthony, S., Carlson, M., Gunnelson, A., Kohler, A.M., Martin, J.G., and Olson, E.R., 2020. ‘Biofluorescence in the platypus (Ornithorhynchus anatinus)’. Mammalia 1 (ahead-of-print).

5. Spinney, L., 2008. ‘Remnants of evolution’. New Scientist 198(2656): 42–45.

6. Shubin, N., 2008. Your Inner Fish. Pantheon.

7. Clack, J.A., and Ahlberg, P.E., 2016. ‘Sarcopterygians: From lobe-finned fishes to the tetrapod stem group’. In Evolution of the Vertebrate Ear ed. J. Clack, R. Fay, and A. Popper, p. 59. Springer Handbook of Auditory Research, 59.

8. Cloutier, R., Clement, A.M., Lee, M.S.Y. et al., 2020. ‘Elpistostege and the origin of the vertebrate hand’. Nature 579: 549–554. https://doi.org/10.1038/s41586-020-2100-8.

9. Braasch, I., Gehrke, A., Smith, J. et al., 2016. ‘The spotted gar genome illuminates vertebrate evolution and facilitates human-teleost comparisons’. Nature Genetics 48: 427–437. https://doi.org/10.1038/ng.3526.

Our Crappy-Crappie Bodies

1. Olshansky, S., Carnes, B., and Butler, R., 2001. ‘If humans were built to last’. Scientific American 284(3): 1–50.

2. Giles, S., Xu, G., Near, T. et al., 2017. ‘Early members of “living fossil” lineage imply later origin of modern ray-finned fishes’. Nature 549: 265–268. https://doi.org/10.1038/nature23654.

3. Stiassny, M.L., Parenti, L.R., and Johnson, G.D., eds. 1996. Interrelationships of Fishes. Academic Press.

4. Hughes, L.C., Ortí, G., Huang, Y., Sun, Y., Baldwin, C.C., Thompson, A.W., Arcila, D., Betancur-R, R., Li, C., Becker, L., and Bellora, N., 2018. ‘Comprehensive phylogeny of ray-finned fishes (Actinopterygii) based on transcriptomic and genomic data’. Proceedings of the National Academy of Sciences 115(24): 6249–6254.

5. Helfman, G.S., Collette, B.B., and Facey, D.E., 1997. The Diversity of Fishes. Blackwell Science.

6. Gemberling, M., Bailey, T.J., Hyde, D.R., and Poss, K.D., 2013. ‘The zebrafish as a model for complex tissue regeneration’. Trends in Genetics 29(11): 611–620.

7. Williams, R., 2010. ‘Thanks be to zebrafish’. Circulation Research 107: 570–572.

8. Diogo, R., Abdala, V., Lonergan, N., and Wood, B.A., 2008. ‘From fish to modern humans—comparative anatomy, homologies and evolution of the head and neck musculature’. Journal of Anatomy 213(4): 391–424, doi:10.1111/j.1469-7580.2008.00953.x.

9. Leite, C.A., Taylor, E.W., Guerra, C.D., Florindo, L.H., Belão, T., and Rantin, F.T., 2009. ‘The role of the vagus nerve in the generation of cardiorespiratory interactions in a neotropical fish, the pacu, Piaractus mesopotamicus’. Journal of Comparative Physiology. A, Neuroethology, sensory, neural, and behavioral physiology 195(8): 721–731. https://doi.org/10.1007/s00359-009-0447-2.

10. Wedel, M.J., 2011. ‘A monument of inefficiency: The presumed course of the recurrent laryngeal nerve in sauropod dinosaurs’. Acta Palaeontologica Polonica 57(2): 251–256.

11. Bryson, B., 2019. The Body: A Guide for Occupants. Random House.

The Tree of Life

1. Fricke, R., Eschmeyer, W.N., and Van Der Laan, R., 2020. ‘Eschmeyer’s catalog of fishes: Genera, species, references’. California Academy of Sciences. http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp.

2. Stork, N.E., McBroom, J., Gely, C., and Hamilton, A.J., 2015. ‘New approaches to narrow global species estimates for beetles, insects, and terrestrial arthropods’. PNAS 112(24): 7519–7523, https://www.pnas.org/content/pnas/112/24/7519.full.pdf.

3. Dykhuizen, D., 2011. ‘Species numbers in bacteria’. Proceedings of the California Academy of Science 56(6 Suppl 1): 62–71. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3160642/.

4. Ocean Metagenomics in PLoS Biology: A collection of articles from the J. Craig Venter Institute’s Global Ocean Sampling expedition. 2007. Special Collection PLoS Biology. https://collections.plos.org/s/file?id=1d/plos_biology_venter_collection_low.pdf.

5. Chakrabarty, P., 2018. ‘Four Billion Years of Evolution in Six Minutes’. Ted.com. https://www.ted.com/talks/prosanta_chakrabarty_four_billion_years_of_evolution_in_six_minutes?language=en.

6. Open Tree of Life (Viewed 2020). One Zoom. http://www.onezoom.org/life.html.

7. Benton, M.J., and Twitchett, R.J., 2003. ‘How to kill (almost) all life: The end-Permian extinction event’. Trends in Ecology & Evolution 18(7): 358–365. https://www.sciencedirect.com/science/article/abs/pii/S0169534703000934

8. May, R.M., and Hawksworth, D.L., 1994. ‘Conceptual aspects of the quantification of the extent of biological diversity’. Philosophical Transactions of the Royal Society 345: 13–20. http://doi.org/10.1098/rstb.1994.0082.

9. Mukherjee, I., Large, R.R., Corkrey, R., and Danyushevsky, L.V., 2018. ‘The boring billion, a slingshot for complex life on earth’. Scientific Reports 8(4432): 4432, doi:10.1038/s41598—018-22695-x.

10. Woese, C.R., Kandler, O., and Wheelis, M.L., 1990. ‘Towards a natural system of organisms: Proposal for the domains Archaea, Bacteria, and Eucarya’. Proceedings of the National Academy of Sciences of the United States of America 87(12): 4576–4579, doi:10.1073/pnas.87.12.4576.

11. Margulis, L. 2011. ‘Symbiogenesis. A new principle of evolution rediscovery of Boris Mikhaylovich Kozo-Polyansky (1890–1957)’. Paleontological Journal 44(12): 1525–1539, doi: 10.1134/S0031030110120087.

12. Theriot, J.A., 2013. ‘Why are bacteria different from eukaryotes?’ BMC Biology 11: 119. https://doi.org/10.1186/1741-7007-11-119.

13. Encyclopaedia Britannica. Category: Logic. (8 August 2007). https://www.britannica.com/topic/category-logic.

14. Aristotle, A., 1986. De Anima (On the Soul). Penguin.

15. Cavanaugh, C.M., Gardiner, S.L., Jones, M.L., Jannasch, H.W., and Waterbury, J.B., 1981. ‘Prokaryotic cells in the hydrothermal vent tube worm Riftia pachyptila Jones: possible chemoautotrophic symbionts’. Science: 340–342.

The Origin of Life

1. Macdougall, D., 2019. Endless Novelties of Extraordinary Interest: The Voyage of H.M.S. Challenger and the Birth of Modern Oceanography. Yale University Press.

2. Zimmer, C., 2021. Life’s Edge: The Search for What it Means to be Alive. Pan Macmillan.

3. Sober, E., 2008. Evidence and Evolution: The Logic Behind the Science. Cambridge University Press.

4. Ranea, J.A.G., Sillero, A., Thornton, J.M., and Orengo, C.A., 2006. ‘Protein superfamily evolution and the Last Universal Common Ancestor (LUCA)’. Journal of Molecular Evolution 63(4): 513–525, doi:10.1007/s00239-005-0289-7.

5. Wolchover, N., 2017. ‘First support for a physics theory of life’. Quanta. https://www.quantamagazine.org/first-support-for-a-physics-theory-of-life-20170726/.

6. Miller, S.L., and Urey, H.C., 1959. ‘Organic compound synthesis on the primitive earth’. Science 130(3370): 245–251.

7. Than, K., 2006. ‘Organic molecules found in diverse space places’. Space.com. http://www.space.com/2711-organic-molecules-diverse-space-places.html.

8. Deamer, D., 2011. First Life: Discovering the Connections Between Stars, Cells, and How Life Began. University of California Press.

9. Cleeves, L.I., Bergin, E.A., Alexander, C.M.D., Du, F., Graninger, D., Öberg, K.I., and Harries, T.J., 2014. ‘The ancient heritage of water ice in the solar system’. Science 345(6204): 1590–1593.

10. Zalasiewicz, J., and Williams, M., 2014. Ocean Worlds: The Story of Seas On Earth and Other Planets. Oxford University Press.

11. Greaves, J.S., Richards, A.M., Bains, W., Rimmer, P.B., Sagawa, H., Clements, D.L., Seager, S., Petkowski, J.J., Sousa-Silva, C., Ranjan, S., and Drabek-Maunder, E., 2020. ‘Phosphine gas in the cloud decks of Venus’. Nature Astronomy: 1–10.

12. Steele, E.J., Qu, J., Gorczynski, R.M., Lindley, R.A., Tokoro, G., Temple, R., and Wickramasinghe, N.C., 2020. ‘Origin of new emergent Coronavirus and Candida fungal diseases—Terrestrial or cosmic?’. Advances in Genetics 106: 75–100.

13. Wald, G., 1957. ‘The origin of optical activity’. Annals of the New York Academy of Sciences 69(2): 352–368, doi: 10.1111/j.1749-6632.1957.tb49671.x.

14. Bailey, J., 2000. ‘Chirality and the origin of life’. Acta Astronautica 46(10–12): 627–631.

15. Brock, T.D., 1997. ‘The value of basic research: discovery of Thermus aquaticus and other extreme thermophiles’. Genetics 146(4): 1207–1210.

16. Baumgartner, R.J., Van Kranendonk, M.J., Wacey, D., Fiorentini, M.L., Saunders, M., Caruso, S., Pages, A., Homann, M., and Guagliardo, P., 2019. ‘Nano-porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life’. Geology 47(11): 1039–1043, doi:10.1130/g46365.1.

The History of Life

1. Lyons, T.W., Droser, M.L., Lau, K.V., Porter, S.M., Xiao, S., and Tang, Q., 2018. ‘After the boring billion and before the freezing millions: Evolutionary patterns and innovations in the Tonian period’. Emerging Topics in Life Sciences 2(2): 161–171. https://doi.org/10.1042/ETLS20170165.

2. McFall-Ngai, M.J., 2015. Giving microbes their due—animal life in a microbially dominant world’. Journal of Experimental Biology 218: 1968–1973, doi: 10.1242/jeb.115121.

3. Hird, S.M., 2017. ‘Evolutionary biology needs wild microbiomes’. Frontiers in Microbiology 8(725). https://www.frontiersin.org/article/10.3389/fmicb.2017.00725.

4. Dethlefsen, L., McFall-Ngai, M., and Relman, D. 2007. ‘An ecological and evolutionary perspective on human–microbe mutualism and disease’. Nature 449: 811–818. https://doi.org/10.1038/nature06245.

5. Lyons, T., Reinhard, C., and Planavsky, N., 2014. ‘The rise of oxygen in Earth’s early ocean and atmosphere’. Nature 506: 307–315. https://doi.org/10.1038/nature13068.

6. Zahnle, K.J., Catling, D.C., and Claire, M.W., 2013. ‘The rise of oxygen and the hydrogen hourglass’. Chemical Geology 362: 26–34, doi: 10.1016/j.chemgeo.2013.08.004.

7. Hodgskiss, M.S.W., Crockford, P.W., Peng, Y., Wing, B.A., and Horner, T.J., 2019. ‘A productivity collapse to end Earth’s Great Oxidation’. Proceedings of the National Academy of Sciences of the United States of America 116(35): 17207–17212, doi: 10.1073/pnas.1900325116.

8. Hemnani, T., and Parihar, M.S., 1998. ‘Reactive oxygen species and oxidative DNA damage’. Indian Journal of Physiology and Pharmacology 42: 440–452.

9. Chen, X., Ling, H., Vance, D. et al., 2015. ‘Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals’. Nature Communications 6: 7142. https://doi.org/10.1038/ncomms8142.

10. Knoll, A.H., 1992. ‘The early evolution of eukaryotes: a geological perspective’. Science 256(5057): 622–627.

11. Runnegar, B., 2000. ‘Loophole for snowball Earth’. Nature 405: 403–404. https://doi.org/10.1038/35013168.

12. Rokas, A., 2008. ‘The molecular origins of multicellular transitions’. Current Opinion in Genetics & Development 18(6): 472–478. https://doi.org/10.1016/j.gde.2008.09.004.

13. King, N., 2004. ‘The unicellular ancestry of animal development’. Developmental Cell 7(3): 313–325. https://doi.org/10.1016/j.devcel.2004.08.010.

14. Morris, S., and Caron, J., 2014. ‘A primitive fish from the Cambrian of North America’. Nature 512: 419–422. https://doi.org/10.1038/nature13414.

15. Morris, S.C., 1989. ‘Burgess shale faunas and the Cambrian Explosion’. Science 246(4928): 339–346.

16. Loron, C.C., François, C., Rainbird, R.H. et al., 2019. ‘Early fungi from the Proterozoic era in Arctic Canada’. Nature 570: 232–235. https://doi.org/10.1038/s41586-019-1217-0.

17. Heckman, D.S., Geiser, D.M., Eidell, B.R., Stauffer, R.L., Kardos, N.L., and Hedges, S.B., 2001. ‘Molecular evidence for the early colonization of land by fungi and plants’. Science 293(5532): 1129–1133.

18. Grosberg, R.K., Vermeij, G.J., and Wainwright, P.C., 2012. ‘Biodiversity in water and on land. Current Biology 22(21): 900–903.

19. Luo, Z. 2007. ‘Transformation and diversification in early mammal evolution’. Nature 450: 1011–1019. https://doi.org/10.1038/nature06277.

20. Janis, C.M., 1993. ‘Tertiary mammal evolution in the context of changing climates, vegetation, and tectonic events’. Annual Review of Earth and Planetary Sciences 24: 467–500.

21. Wilson, D.E., and Reeder, D.M., 2005. Mammal Species of the World: A Taxonomic and Geographic Reference. Johns Hopkins University Press.

22. Hawks, J., and Berger, L., 2020. ‘Homo naledi and its significance in evolutionary anthropology’. In Theology and Evolutionary Anthropology: Dialogues in Wisdom, Humility and Grace, ed. Celia Deane-Drummond and Agustín Fuentes. Routledge.

23. Andrews, P., and Harrison, T., 2005. ‘The last common ancestor of apes and humans’. Interpreting the Past: Essays on Human, Primate, and Mammal Evolution in Honor of David Pilbeam: 103–121.

24. Bar-On, Y.M., Phillips, R., and Milo, R., 2018. ‘The biomass distribution on Earth’. Proceedings of the National Academy of Sciences 115(25): 6506–6511, doi: 10.1073/pnas.1711842115.

PART IV: Why Understanding Evolution Matters

Evolution in the Anthropocene (Design and CRISPR-Cas9)

1. Van Valkenburgh, B., 2007. ‘Déjà vu: The evolution of feeding morphologies in the Carnivora’. Integrative and Comparative Biology 47: 147–163.

2. Sargan, D., 2018. ‘Ethics and genetics of brachycephalic breeding: Can they all be bad?’. British Small Animal Veterinary Association Congress Proceedings: 370–371, doi: 10.22233/9781910443590.50.1.

3. Wang, J., Hill, W.G., Charlesworth, D., and Charlesworth, B., 1999. ‘Dynamics of inbreeding depression due to deleterious mutations in small populations: mutation parameters and inbreeding rate’. Genetics Research 74(2): 165–178.

4. Wolf, A.P., 2005. Inbreeding, Incest, and the Incest Taboo: The State of Knowledge at the Turn of the Century. Stanford University Press.

5. Jiang, F., and Doudna, J.A., 2017. ‘CRISPR-Cas9 structures and mechanisms’. Annual Review of Biophysics 46(1): 505–529.

6. Buchman, A., Gamez, S., Li, M., Antoshechkin, I., Li, H., Wang, H., Chen, C., Klein, M.J., Duchemin, J., Paradkar, P.N., and Akbari, O.S., 2019. ‘Engineered resistance to Zika virus in transgenic Aedes aegypti expressing a polycistronic cluster of synthetic small RNAs’. Proceedings of the National Academy of Sciences 116(9): 3656–3661, doi: 10.1073/pnas.1810771116.

7. Scudellari, M., 2019. ‘Self-destructing mosquitoes and sterilized rodents: The promise of gene drives’. Nature 571: 160–162, doi: 10.1038/d41586-019-02087-5.

8. Bosley, K.S., Botchan, M., Bredenoord, A.L., Carroll, D., Charo, R.A., Charpentier, E., Cohen, R., Corn, J., Doudna, J., Feng, G., and Greely, H.T., 2015. ‘CRISPR germline engineering—the community speaks’. Nature Biotechnology 33(5): 478–486.

9. Baltimore, D., Berg, P., Botchan, M., Carroll, D., Charo, R.A., Church, G., Corn, J.E., Daley, G.Q., Doudna, J.A., Fenner, M., and Greely, H.T., 2015. ‘A prudent path forward for genomic engineering and germline gene modification’. Science 348(6230): 36–38.

10. Doudna, J., 2015. ‘Genome-editing revolution: My whirlwind year with CRISPR’. Nature News 528(7583): 469.

11. Tiwari, S., Kaur, N., and Awasthi, P., 2020. ‘Fruit crops improvement using CRISPR/Cas9 system’. Genome Engineering via CRISPR-Cas9 System: 131–145, doi:10.1016/b978-0-12-818140-9.00012-x.

12. Knowles, T.G., Kestin, S.C., Haslam, S.M., Brown, S.N., Green, L.E., Butterworth A. et al., 2008. ‘Leg disorders in broiler chickens: Prevalence, risk factors and prevention’. PLoS ONE 3(2): e1545. https://doi.org/10.1371/journal.pone.0001545.

13. Taitingfong, R.I., 2017. ‘Islands as laboratories: Indigenous knowledge and gene drives in the Pacific’. Human Biology. Project MUSE. https://muse.jhu.edu/article/749634/summary.

14. Wong, M.C., Cregeen, S.J.J., Ajami, N.J., and Petrosino, J.F., 2020. ‘Evidence of recombination in coronaviruses implicating pangolin origins of nCoV-2019’. bioRxiv. https://doi.org/10.1101/2020.02.07.939207.

15. Andersen, K.G., Rambaut, A., Lipkin, W.I. et al., 2020. ‘The proximal origin of SARS-CoV-2’. Nature Medicine 26: 450–452. https://doi.org/10.1038/s41591-020-0820-9.

16. Simberloff, D., Schmitz, D.C., and Brown, T.C., 1997. Strangers in Paradise: Impact and Management Of Nonindigenous Species In Florida. Washington (DC) Island Press.

17. Adhikari, D. et al., 2015. ‘Modelling hotspots for invasive alien plants in India’. PLoS ONE 10(7).

18. Ankila Hiremath, J., and Krishnan, S., 2016. ‘India knows its invasive species problem but this is why nobody can deal with it properly’. The Wire.

19. Zimmer, C., 2018. She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity. Dutton.

20. Kleiderman, E., and Ogbogu, U., 2019. ‘Realigning gene editing with clinical research ethics: What the ‘CRISPR Twins’ debacle means for Chinese and international research ethics governance’. Accountability in Research 26(4): 257–264, doi: 10.1080/08989621.2019.1617138.

21. Harari, Y.N., 2015. Homo Deus: A Brief History of Tomorrow. Harvill Secker.

22. Maron, D.F., 2018. ‘Under poaching pressure, elephants are evolving to lose their tusks’. National Geographic.com, https://www.nationalgeographic.com/animals/2018/11/wildlife-watch-news-tuskless-elephants-behavior-change/#.

23. Ellis, R., 2008. ‘The bluefin in peril’. Scientific American 298(3): 70–77. www.jstor.org/stable/26000519. Accessed 6 April 2020.

24. Piper, R., 2009. Extinct Animals: An Encyclopedia of Species that Have Disappeared During Human History. Greenwood Press.

25. Leakey, R.E., and Lewin, R., 1996. The Sixth Extinction: Patterns of Life and the Future of Humankind. Anchor.

26. Ceballos, G., Ehrlich, P.R., Barnosky, A.D., García, A., Pringle, R.M., and Palmer, T.M., 2015. ‘Accelerated modern human-induced species losses: Entering the sixth mass extinction’. Science Advances 1(5): p.e1400253.

27. Turvey, S.T., and Crees, J.J., 2019. ‘Extinction in the Anthropocene’. Current Biology 29(19): R982–R986.

28. Pimm, S., and Raven, P., 2000. ‘Extinction by numbers’. Nature 403: 843–845. https://doi.org/10.1038/35002708.

29. Kolbert, E., 2014. The Sixth Extinction: An Unnatural History. A&C Black.

30. Brooks, T.M., Mittermeier, R.A., Mittermeier, C.G., da Fonseca, G.A.B., Rylands, A.B., Konstant, W.R., Flick, P., Pilgrim, J., Oldfield, S., Magin, G., and Hilton-Taylor, C., 2002. ‘Habitat loss and extinction in the hotspots of biodiversity’. Conservation Biology 16(4): 909–923, doi: 10.1046/j.1523-1739.2002.00530.x.

31. Gaynor, K.M., Hojnowski, C.E., Carter, N.H., and Brashares, J.S., 2018. ‘The influence of human disturbance on wildlife nocturnality’. Science 360(6394): 1232–1235.

32. Crutzen, P.J. 2006. ‘The “Anthropocene”’. In Earth System Science in the Anthropocene. Springer.

33. Osaka, S., 2020. ‘The world is on lockdown. So where are all the carbon emissions coming from?’. Grist. https://grist.org/climate/the-world-is-on-lockdown-so-where-are-all-the-carbon-emissions-coming-from/.

Natural History

1. Bush, V., 1945. ‘Science, the Endless Frontier: A report to the President’. US Government Printing Office. https://www.nsf.gov/about/history/vbush1945.htm.

2. Morris, E., 2019. Edison. Penguin Random House.

3. Rocha, L. et al., 2014. ‘Specimen collection: An essential tool’. Science 344: 814–815.

4. Lendemer, J., Thiers, B., Monfils, A.K., Zaspel, J., Ellwood, E.R., Bentley, A., LeVan, K., Bates, J., Jennings, D., Contreras, D., and Lagomarsino, L., 2020. ‘The extended specimen network: A strategy to enhance US biodiversity collections, promote research and education’. BioScience 70(1): 23–30.

5. Buckner, J.C., Sanders, R.C., Faircloth, B.C., and Chakrabarty, P., 2021. ‘Science Forum: The critical importance of vouchers in genomics’. Elife 10: e68264.

6. Goodwin, Z.A., Harris, D.J., Filer, D., Wood, J.R., and Scotland, R.W., 2015. ‘Widespread mistaken identity in tropical plant collections’. Current Biology 25(22): R1066–R1067.

7. Larsson, E., 2019. ‘Collecting, Curating and the Construction of Zoological Knowledge: Walter Rothschild’s Zoological Enterprise, c. 1878–1937’. Ph.D. Thesis, King’s College London.

8. Kemp, C., 2017. ‘The financier who bought all of nature’. New Scientist 3150: 40–41.

9. Johnson, K.W., 2018. The Feather Thief: Beauty, Obsession, and the Natural History Heist of the Century. Penguin.

10. Chakrabarty, P., Davis, M.P., Smith, W.L., Baldwin, Z.H., and Sparks, J.S., 2011. ‘Is sexual selection driving diversification of the bioluminescent ponyfishes (Teleostei: Leiognathidae)?’ Molecular Ecology 20: 2818–2834.

11. Cashion, T., Le Manach, F., Zeller, D., and Pauly, D., 2017. ‘Most fish destined for fishmeal production are food-grade fish’. Fish and Fisheries 18(5): 837–844. https://doi.org/10.1111/faf.12209.

12. Kauhala, K., Talvitie, K., and Vuorisalo, T., 2015. ‘Free-ranging house cats in urban and rural areas in the north: Useful rodent killers or harmful bird predators?’. Journal of Vertebrate Biology 64(1): 45–55.

13. Loss, S.R., Will, T., and Marra, P.P., 2013. ‘The impact of free-ranging domestic cats on wildlife of the United States’. Nature Communications 4: 1396. http://dx.doi.org/10.1038/ncomms2380.

14. Wong, K., 2001. ‘Mother Nature’s medicine cabinet’. Scientific American. https://www.scientificamerican.com/article/mother-natures-medicine-c/.

15. DiEuliis, D., Johnson, K.R., Morse, S.S., and Schindel, D.E., 2016. ‘Opinion: Specimen collections should have a much bigger role in infectious disease research and response’. Proceedings of the National Academy of Sciences 113(1): 4–7, doi: 10.1073/pnas.1522680112.

16. Warny, S., Ferguson, S., Hafner, M.S., and Escarguel, G., 2019. ‘Using museum pelt collections to generate pollen prints from high-risk regions: A new palynological forensic strategy for geolocation’. Forensic Science International 306(110061), doi: 10.1016/j.forsciint.2019.110061.

17. Drew, J., 2011. ‘The role of natural history institutions and bioinformatics in conservation biology’. Conservation Biology 25: 1250–1252, doi: 10.1111/j.1523-1739.2011.01725.x.

18. Das, S., and Lowe, M., 2018. ‘Nature read in black and white: Decolonial approaches to interpreting natural history collections’. Journal of Natural Science Collections 6: 4–14.

19. De Vos, A., 2020. ‘The problem of “Colonial Science”’. Scientific American. https://www.scientificamerican.com/article/the-problem-of-colonial-science/.

20. Ndunguru, J., Tairo, F., Boykin, L., and Sseruwagi, P., 2019. ‘Principles of effective collaboration in agricultural development and research for impact’. AgriRxiv, doi: 10.31220/osf.io/udf63.

21. Fontaine, B., van Achterberg, K., Alonso-Zarazaga, M.A. et al., 2012. ‘New species in the Old World: Europe as a frontier in biodiversity exploration, a test bed for 21st century taxonomy’. PLoS One 7(5): 36881, doi: 10.1371/journal.pone.0036881.

22. Brusatte, S., 2018. The Rise and Fall of the Dinosaurs: A New History of a Lost World. HarperCollins.

Our Genealogy and Ancestry

1. Mack, K., 2020. The End of Everything: Astrophysics and the Ultimate Fate of the Cosmos. Scribner.

2. Edmonds, P., 2018. ‘These twins will make you rethink race’. National Geographic. https://www.nationalgeographic.com/magazine/2018/04/race-twins-black-white-biggs/.

3. Woodson, J., 2016. Brown Girl Dreaming. Puffin Books, Penguin Random House.

4. Coop, G., 2013. ‘How much of your genome do you inherit from a particular grandparent?’. Gcbias. https://gcbias.org/2013/10/20/how-much-of-your-genome-do-you-inherit-from-a-particular-grandparent/.

5. Enard, D., and Petrov, D.A., 2018. ‘Evidence that RNA Viruses drove adaptive introgression between Neanderthals and Modern Humans’. Cell 175(2): 360–371.e13, doi: 10.1016/j.cell.2018.08.034.

6. Gazal, S., Sahbatou, M., Babron, M.C., Génin, E., and Leutenegger, A.L., 2015. ‘High level of inbreeding in final phase of 1000 Genomes Project’. Scientific Reports 5: 17453.

7. Horton, A., 2018. ‘Elizabeth Warren angers prominent Native Americans with politically fraught DNA test’. The Washington Post. https://www.washingtonpost.com/nation/2018/10/16/elizabeth-warren-angers-prominent-native-americans-with-politically-fraught-dna-test/.

8. Garrison, N.A., 2018. ‘Genetic ancestry testing with tribes: ethics, identity & health implications’. Daedalus 147(2): 60–69. https://doi.org/10.1162/DAED_a_00490.

9. Wagner, J.K., 2010. ‘Interpreting the implications of DNA ancestry tests’. Perspectives in Biology and Medicine 53(2): 231–248, doi: 10.1353/pbm.0.0158.

10. Hilleary, C., 2018. ‘Native Americans speak out on Elizabeth Warren DNA controversy’. Voice of America. https://www.voanews.com/a/native-americans-speak-out-on-elizabeth-warren-dna-controversy/4615743.html?fbclid=IwAR2WaKcxC3G52su9AncvZTHRj35RY3vAgl4-7tAt8I0xZyCjeixxe77Ae0A.

11. Chakrabarty, P., 2020. ‘What can DNA tests really tell us about our ancestry?’. TED-Ed. https://www.ted.com/talks/prosanta_chakrabarty_what_can_dna_tests_really_tell_us_about_our_ancestry?language=en.

12. Auton, A., Brooks, L.D., Durbin, R.M., Garrison, E.P., Kang, H.M., Korbel, J.O. et al., 2015. ‘A global reference for human genetic variation’. Nature 526(7571): 68–74. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750478/.

13. ‘Ancestry Composition: 23andMe’s State-of-the-Art Geographic Ancestry Analysis’. (viewed 2020). 23andMe.com. https://www.23andme.com/ancestry-composition-guide/.

14. Cann, H.M. et al., 2002. ‘A human genome diversity cell line panel’. Science 296(5566): 261–262, doi: 10.1126/science.296.5566.261b.

15. Durbin, R., Altshuler, D., Durbin, R. et al., 2010. ‘A map of human genome variation from population-scale sequencing’. Nature 467: 1061–1073. https://doi.org/10.1038/nature09534.

16. Hamon, A., 2018. why white supremacists are chugging milk (and why geneticists are alarmed). The New York Times. https://www.nytimes.com/2018/10/17/us/white-supremacists-science-dna.html.

17. Hamon, A., 2018. ‘Geneticists criticize use of science by white nationalists to justify “racial purity”’. The New York Times. https://www.nytimes.com/2018/10/19/us/white-supremacists-science-genetics.html.

18. Sta?nescu, V., 2018. ‘“White power milk”: Milk, dietary racism, and the “alt-right”’. Animal Studies Journal 7(2): 103–128.

19. Singh, P., Arora, A., Strand, T.A., Leffler, D.A., Catassi, C., Green, P.H., Makharia, G.K. et al., 2018. ‘Global prevalence of celiac disease: Systematic review and meta-analysis’. Clinical Gastroenterology and Hepatology 16(6): 823–836.e2, doi: 10.1016/j.cgh.2017.06.037.

20. Gerbault, P., Liebert, A., Itan, Y. et al., 2011. ‘Evolution of lactase persistence: An example of human niche construction’. Philosophical Transactions of the Royal Society B: Biological Sciences 366(1566): 863–877, doi: 10.1098/rstb.2010.0268.

21. ‘ASHG denounces attempts to link genetics and racial supremacy’. 2018. The American Journal of Human Genetics 103: 636, doi: 10.1016/j.ajhg.2018.10.011.

22. Saini, A., 2019. Superior: The Return of Race Science. Beacon Press, Fourth Estate Books.

23. Lewontin, R.C., 1972. ‘The apportionment of human diversity’. In Evolutionary Biology. Springer.

24. Yudell, M., Roberts, D., DeSalle, R., and Tishkoff, S., 2016. ‘Taking race out of human genetics’. Science 351(6273): 564–565, doi: 10.1126/science.aac4951.

25. Zimmerman, R.S., Vega, W.A., Gil, A.G., Warheit, G.J., Apospori, E., and Biafora, F., 1994. ‘Who is Hispanic? Definitions and their consequences’. American Journal of Public Health 84(12): 1985–1987. https://doi.org/10.2105/AJPH.84.12.1985.

26. Salinas Jr., C., and Lozano, A., 2019. ‘Mapping and recontextualizing the evolution of the term Latinx: An environmental scanning in higher education’. Journal of Latinos and Education 18(4): 302–315, doi: 10.1080/15348431.2017.1390464.

27. Lee, D.N., 2020. ‘Diversity and inclusion activisms in animal behaviour and the ABS: A historical view from the USA’. Animal Behaviour. doi.org/10.1016/j.anbehav.2020.03.019.

28. Graves, J.L., 2019. ‘African Americans in evolutionary science: Where we have been, and what’s next’. Evolution: Education and Outreach 12(18). https://doi.org/10.1186/s12052-019-0110-5.

29. Barber, P.H., Hayes, T.B., Johnson, T.L., and Márquez-Magaña, L., 2020. ‘Systemic racism in higher education’. Science, 369(6510): 1440–1441.

30. Claw, K.G., Anderson, M.Z., Begay, R.L. et al., 2018. ‘A framework for enhancing ethical genomic research with Indigenous communities’. Nature Communications 9(2957). https://doi.org/10.1038/s41467-018-05188-3.

31. Bates, C., 1995. ‘Race, caste and tribe in central India: The early origins of Indian anthropometry’. In The Concept of Race in South Asia, ed. P. Robb, pp. 219–259. Oxford University Press.

32. Ghurye, G.S., 1969. Caste and Race in India. Popular Prakashan.

33. Baharian, S., Barakatt, M., Gignoux, C.R. et al., 2016. ‘The Great Migration and African–American genomic diversity’. PLoS Genet 12(5): 1006059, doi: 10.1371/journal.pgen.1006059.

34. Lelyveld, J., 2012. Great Soul: Mahatma Gandhi and His Struggle with India. Vintage.

35. Davis, F.J., 1991. Who Is Black? One Nation’s Definition. Pennsylvania State University Press.

36. AP Stylebook. 23 June 2020. https://www.apstylebook.com/race-related-coverage.

37. Graves Jr., J.L., 2015. ‘Why the nonexistence of biological races does not mean the nonexistence of racism’. American Behavioral Scientist 59(11): 1474–1495.

Sex/Gender/Sexuality

1. Barazani, Y., and Sabanegh, E. Jr., 2015. ‘Rare case of monozygotic twins diagnosed with klinefelter syndrome during evaluation for infertility’. Nature Reviews Urology 17(1): 42–45.

2. Reiss, A.L., Freund, L., Plotnick, L., Baumgardner, T., Green, K., Sozer, A.C., Reader, M., Boehm, C., and Denckla, M.B., 1993. ‘The effects of X monosomy on brain development: Monozygotic twins discorcant for Turner’s syndrome’. Annals of Neurology 34(1): 95–107, doi: 10.1002/ana.410340117.

3. Montañez, A., 2017. ‘Beyond XX and XY’. Scientific American 317(3): 50–51, doi: 10.1038/scientificamerican0917-50.

4. Hughes, I.A., Davies, J.D., Bunch, T.I., Pasterski, V., Mastroyannopoulou, K., and MacDougall, J., 2012. ‘Androgen insensitivity syndrome’. The Lancet 380(9851): 1419–1428.

5. Fausto-Sterling, A., 2000. Sexing the Body: Gender Politics and the Construction of Sexuality. Basic Books.

6. Roughgarden, J., 2009. Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press.

7. Gonçalves, D., Oliveira, R.F., Körner, K., and Schlupp, I., 2003. ‘Intersexual copying by sneaker males of the peacock blenny’. Animal Behaviour 65(2): 355–361, doi: 10.1006/anbe.2003.2065.

8. Hanlon, R., Naud, M., Shaw, P. et al., 2005. ‘Transient sexual mimicry leads to fertilization’. Nature 433: 212. https://doi.org/10.1038/433212a.

9. Casas, L., Saborido-Rey, F., Ryu, T., Michell, C., Ravasi, T., and Irigoien, X., 2016. ‘Sex change in clownfish: Molecular insights from transcriptome analysis’. Scientific Reports 6: 35461. https://doi.org/10.1038/srep35461.

10. Imperato-McGinley, J., Guerrero, L., Gautier, T., and Peterson, R.E., 1974. ‘Steroid 5alpha-reductase deficiency in man: An inherited form of male pseudohermaphroditism’. Science 186(4170): 1213–1215, doi: 10.1126/science.186.4170.1213.

11. Nutt, A.E., 2016. Becoming Nicole. Penguin Random House.

12. Peletz, M.G., 2009. Gender Pluralism: Southeast Asia Since Early Modern Times. Routledge.

13. Bell, J.T., and Spector, T.D., 2012. ‘DNA methylation studies using twins: What are they telling us?’. Genome Biology 13(10): 172, doi: 10.1186/gb-2012-13-10-172.

14. Diamond, M., 2013. ‘Transsexuality among twins: Identity concordance, transition, rearing, and orientation’. International Journal of Transgenderism 14(1): 24–38, doi: 10.1080/15532739.2013.750222.

15. Ngun, T.C., and Vilain, E., 2014. ‘The biological basis of human sexual orientation’. Advances in Genetics 86: 167–184, doi: 10.1016/b978-0-12-800222-3.00008-5.

16. Ganna, A., Verweij, K.J.H., Nivard, M.G. et al., 2019. ‘Large-scale GWAS reveals insights into the genetic architecture of same-sex sexual behavior’. Science 365(6456).

17. Sommer, V., and Vasey, P.L., 2006. Homosexual Behaviour in Animals: An Evolutionary Perspective. Vasey Cambridge University Press.

18. Bagemihl, B., 2000. Exuberance: Animal Homosexuality and Natural Diversity. Stonewall Inn Editions Paperback.

19. Bull, C., 2002. ‘Birds of a feather: Meet Wendell and Cass, the gay male penguin couple at the New York Aquarium’. The Advocate. Retrieved 22 April 2012.

20. Ebeling, K.S., and Spanier, B.B., 2011. ‘What made those penguins gay?’. In Gender and the Science of Difference: Cultural Politics of Contemporary Science and Medicine, ed. Jill A. Fisher, pp. 126–144. Rutgers University Press.

21. Yoder, J., 2019. ‘A new age of gay genomics is here. Are we ready for the consequences?’. Slate. https://slate.com/technology/2019/08/gay-gene-study-ganna-biobank-23andme-risks.html.

22. Burki, T., 2020. ‘Genetic apps: raising more questions than they answer?’ The Lancet, Digital Health 2(1): 13–14. https://www.thelancet.com/journals/landig/issue/vol2no1/PIIS2589-7500(19)X0010-2.

23. Hill, W.D., Davies, N.M., Ritchie, S.J. et al., 2019. ‘Genome-wide analysis identifies molecular systems and 149 genetic loci associated with income’. Nature Communications 10: 5741. https://doi.org/10.1038/s41467-019-13585-5.

24. Lee, J.J., Wedow, R., Okbay, A. et al., 2018. ‘Gene discovery and polygenic prediction from a genome-wide association study of educational attainment in 1.1 million individuals’. Nature Genetics 50: 1112–1121. https://doi.org/10.1038/s41588-018-0147-3.

25. Keely, K., 2002. ‘Poverty, sterilization, and eugenics in Erskine Caldwell’s Tobacco Road’. Journal of American Studies 36(1): 23–42, doi: 10.1017/S002187580200676X.

26. Hall, E., 2019. Aristotle’s Way: How Ancient Wisdom Can Change Your Life. Penguin Press.

27. Cultotta, E., 2019. ‘Probing an evolutionary riddle’. Science 365(6455): 748–749.

28. Monk, J.D., Giglio, E., Kamath, A., Lambert, M.R., and McDonough, C.E., 2019. ‘An alternative hypothesis for the evolution of same-sex sexual behaviour in animals’. Nature: Ecology & Evolution: 1–10.

29. Gates, G.J., 2011. ‘How many people are gay, lesbian, bisexual and transgender?’. The Williams Institute. https://williamsinstitute.law.ucla.edu/publications/how-many-people-lgbt/.

30. Shahani, P. 2020. Queeristan: LGBTQ Inclusion in the Indian Workplace. Westland Business.

31. McKnight, J., 1997. Straight Science? Homosexuality, Evolution and Adaptation. Psychology Press.

32. Casci, T. 2004. ‘Gay genes boost fertility’. Nature Reviews Genetics 5: 884. https://doi.org/10.1038/nrg1510.

33. McKnight, J., and Malcolm, J., 2000. ‘Is male homosexuality maternally linked?’. Psychology, Evolution & Gender 2(3): 229–252, doi: 10.1080/14616660010024599.

34. Wilson, E.O., 1975. Sociobiology The New Synthesis, Twenty-Fifth Anniversary Edition. Harvard University Press.

35. Roughgarden, J., 2017. ‘Homosexuality and evolution’. On Human Nature: 495–516, doi: 10.1016/b978-0-12-420190-3.00030-2.

36. Jones, S. Webster, A.J., and Zemnick, A.T., 2019. ‘Inclusive and accurate methods for teaching sex- and gender-related topics [Google slides]’. Retrieved from https://projectbiodiversify.org/sex/.

BOX 2: Sexual Selection of Something Else?

1. Darwin, C., 1859. On the Origin of Species by Means of Natural Selection, or Preservation of Favoured Races in the Struggle for Life. John Murray.

2. Darwin, C., 1896. The Descent of Man and Selection in Relation to Sex. D. Appleton.

3. Wilcox, C. 2020. ‘Males are the taller sex. Estrogen, not fights for mates, may be why’. Quanta Magazine.

4. Dunsworth, H.M., 2020. ‘Expanding the evolutionary explanations for sex differences in the human skeleton’. Evolutionary Anthropology: Issues, News, and Reviews.

5. Kokko, H., Jennions, M.D., and Brooks, R., 2006. ‘Unifying and testing models of sexual selection’. Annual Review of Ecology, Evolution, and Systematics 37: 43–66.

6. Andersson, M., 1994. Sexual Selection (Vol. 72). Princeton University Press.

7. Rosenqvist, G., 1990. ‘Male mate choice and female-female competition for mates in the pipefish Nerophis ophidion’. Animal Behaviour 39(6): 1110–1115.

8. Giroux, M.A., Ditlecadet, D., Martin, L.J., Lanctot, R.B., and Lecomte, N., 2016. ‘Sexing a sex-role-reversed species based on plumage: Potential challenges in the red phalarope’. PeerJ 4: p.e1989.

Combatting Post-truth with Trust

1. Swartz, T.H., Palermo, A.G.S., Masur, S.K., and Aberg, J.A., 2019. ‘The science and value of diversity: Closing the gaps in our understanding of inclusion and diversity’. The Journal of Infectious Diseases 220(Supplement_2): S33–S41.

2. Reid, A.J., Eckert, L.E., Lane, J.F., Young, N., Hinch, S.G., Darimont, C.T., Cooke, S.J., Ban, N.C., and Marshall, A., 2020. ‘“Two-Eyed Seeing”: An Indigenous framework to transform fisheries research and management’. Fish and Fisheries 22: 243–261.

3. Roy, R.D., 2018. ‘Decolonise science—time to end another imperial era’. The Conversation 5 April.

4. Lundgren, L., Stofer, K., Dunckel, B., Krieger, J., Lange, M., and James, V., 2019. ‘Panel-based exhibit using participatory design elements may motivate behavior change’. Journal of Science Communication 18(2): A03.

5. Heigl, F., Kieslinger, B., Paul, K.T., Uhlik, J., and Dörler, D., 2019. ‘Opinion: Toward an international definition of citizen science’. Proceedings of the National Academy of Sciences 116(17): 8089–8092. doi.org/10.1073/pnas.
1903393116.

6. Aristeidou, M., and Herodotou, C., 2020. ‘Online citizen science: A systematic review of effects on learning and scientific literacy’. Citizen Science: Theory and Practice 5(1): 11.

Comments from/Conversations with/Creationists

1. Pray, L., 2008. ‘Eukaryotic genome complexity’. Nature Education 1(1): 96.

2. Ashworth, H., 2020. ‘How long is your DNA?’. Science Focus. https://www.sciencefocus.com/the-human-body/how-long-is-your-dna/.

Epilogue

1. Brady, J.S., 2020. Remarks by President Trump, Vice President Pence, and Members of the Coronavirus Task Force in Press Briefing. Whitehouse.gov. https://www.whitehouse.gov/briefings-statements/remarks-president-trump-vice-president-pence-members-coronavirus-task-force-press-briefing-24/.

2. Kennedy, D.A., and Read, A.F., 2020. ‘Monitor for COVID-19 vaccine resistance evolution during clinical trials’. PLoS Biology 18(11): e3001000.

3. Chotiner, I., 2020. ‘The contrarian coronavirus theory that informed the Trump administration’. The New Yorker. https://www.newyorker.com/news/q-and-a/the-contrarian-coronavirus-theory-that-informed-the-trump-administration.

4. Epstein, R., 2020. ‘Coronavirus perspective’. The Hoover Institute. https://www.hoover.org/research/coronavirus-pandemic.

5. Kalish, H., Klumpp-Thomas, C., Hunsberger, S., Baus, H.A., Fay, M.P., Siripong, N., Wang, J., Hicks, J., Mehalko, J., Travers, J., Drew, M., Sadtler, K. et al., 2021. ‘Undiagnosed SARS-CoV-2 seropositivity during the first six months of the COVID-19 pandemic in the United States’. Science Translational Medicine 13: eabh3826.

6. Wasik, B., and Murphy, M., 2012. Rabid: A Cultural History of the World’s Most Diabolical Virus. Penguin.

7. Mehta, P., McAuley, D.F., Brown, M., Sanchez, E., Tattersall, R.S., and Manson, J.J., 2020. ‘COVID19: Consider cytokine storm syndromes and immunosuppression’. Lancet. https://doi.org/10.1016/S0140 6736(20)30628 0.

8. Spinney, L., 2017. Pale Rider: The Spanish Flu of 1918 and How It Changed the World. Public Affairs.

9. Shah, S., 2016. Pandemic: Tracking Contagions from Cholera to Ebola and Beyond. Sarah Crichton Books.

10. Zimmer, C., 2020. ‘Most New York coronavirus cases came from Europe, genomes show’. The NY Times. https://www.nytimes.com/2020/04/08/science/new-york-coronavirus-cases-europe-genomes.html.

11. Mehta, S., 2020. ‘Trump’s touting of “racehorse theory” tied to eugenics and Nazis alarms Jewish leaders’. Los Angeles Times. https://www.latimes.com/politics/story/2020-10-05/trump-debate-white-supremacy-racehorse-theory.

12. Wu, N., 2020. ‘Trump criticized for praising “good bloodlines” of Henry Ford, who promoted anti-Semitism’. USA Today. https://www.usatoday.com/story/news/politics/
2020/05/22/trump-criticized-praising-bloodlines-henry-ford-anti-semite/5242361002/.

13. Sohini, C., 2019. ‘Bowel cleanse for better DNA: The nonsense science of Modi’s India’. This Week in Asia. https://www.scmp.com/week-asia/society/article/2181752/bowel-cleanse-better-dna-nonsense-science-modis-india.

Glossary

1. Waltz, E., 2015. ‘Nonbrowning GM apple cleared for market’. Nature Biotechnology 33(4): 326–328.

2. Hutton, J., 1795. Theory of the Earth: With Proofs and Illustrations (Vol. 1). Library of Alexandria.

3. Lyell, C., and Deshayes, G.P., 1830. Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth’s Surface, By Reference to Causes Now in Operation (Vol. 1). J. Murray.

4. Genesis: King James Bible.

5. Numbers, R.L., 2006. The Creationists: From Scientific Creationism to Intelligent Design (No. 33). Harvard University Press.

6. Funk, C., Rainie, L., and Page, D., 2015. ‘Americans, politics and science issues’. Pew Research Center 1.

Further Reading

Learn more about the science of evolution from Ed Yong, Carl Zimmer, Deborah Blum, Eugenie Scott, Shaena Montanari, Katherine Wu, Amanda Glaze-Crampes, Mary Jane West-Eberhard, David Quammen, P.Z. Myers, Danielle Lee, Anna Rothschild, Emily Graslie, C. Brandon Ogbunu, Andrea Reid, Keolu Fox, Laura Boykin, Neil Shubin, Raghavendra Gadagkar, Richard Conniff, Hope Jahren, Mohamed Noor, Leslie Rissler, Scott Solomon, Helen Scales, David Shiffman, Riley Black, Jonathan Eisen, Jeremy Yoder, Jonathan Losos, Jessica Ware, Richard Lenski, Ken Miller, Christie Wilcox, Joseph L. Graves Jr., Hopi Hoekstra, Douglas Futuyma and many other wonderful scientists, explorers, and thinkers.

Figure Credits

Cover Art: Image by Akangksha Sarmah.

Figure 1: Image by Sumantra Mukherjee. DNA test results mine, from Vitagene.

Figure 2A and 2B: Images from Shutterstock and T. Michael Keesey (PhyloPic.org). Image by Prosanta Chakrabarty and John McCormack (with permission).

Figure 3: Image by Prosanta Chakrabarty with silhouettes from PhyloPic.org. Shark—No copyright http://phylopic.org/image/545d45f0-0dd1-4cfd-aad6-2b835223ea0d/; Fish—http://phylopic.org/image/f1f91d08-b850-4600-ad64-622ce87f0199/; Seahorse—http://phylopic.org/image/1ce0d9a9-c644-4cc6-b4b3-02e2e7aa2266/.

Figure 4: Image by Sumantra Mukherjee.

Figure 5: Modified from Hug, Laura A., Baker, Brett J., Anantharaman, Karthik, Brown, Christopher T., Probst, Alexander J., Castelle, Cindy J., Butterfield, Cristina N., Hernsdorf, Alex W., Amano, Yuki, Ise, Kotaro, Suzuki, Yohey, Dudek, Natasha, Relman, David A., Finstad, Kari M., Amundson, Ronald, Thomas, Brian C., and Banfield, Jillian F. ‘A new view of the tree of life’. Nature Microbiology 1(16048) (11 April 2016). doi: 10.1038/nmicrobiol.2016.48.

Free to reprint - https://creativecommons.org/licenses/by/4.0/(B) simplified tree from Wikipedia https://en.wikipedia.org/wiki/Phylogenetic_tree.

Figure 6: Image by Sumantra Mukherjee.

Figures 7A and 7B: Image by Prosanta Chakrabarty. Portions of silhouette images from T. Michael Keesey and PhyloPic.org.

Figure 8: Image by Sumantra Mukherjee.

Figure 9: Image by Sumantra Mukherjee.

Figure 10: Image by Sumantra Mukherjee.

Figure 11: Image by Sumantra Mukherjee.

Figure 12: Image by Prosanta Chakrabarty.

Figure 13: Image by Sumantra Mukherjee.

Figure 14: Creative Commons 3: Reprinted from Braasch, I., Gehrke, A., Smith, J. et al. ‘The spotted gar genome illuminates vertebrate evolution and facilitates human-teleost comparisons’. Nature Genetics 48 (2016): 427–437. https://doi.org/10.1038/ng.3526.

Figure 15: Photo of Bessie; taken by the author. She has since quit smoking; which is not easy for Frenchies to do.

DARWIN MOVIE PANELS: ‘From So Simple a Beginning’ All illustrations from Ethan Kocak, created by him for this book.

About the Author

Dr. Prosanta Chakrabarty is a Professor and the Curator of Fishes at the Museum of Natural Science and Department of Biological Sciences at Louisiana State University. He is also a Research Associate at the American Museum of Natural History in New York, Smithsonian’s National Museum of Natural History in Washington, DC, and the Canadian Museum of Nature in Ottawa. He is a systematist and an ichthyologist studying the evolution and biogeography of both freshwater and marine fishes. His work has taken him to more than thirty countries around the world (including Japan, Australia, Brazil, Taiwan, Madagascar, Panama and Kuwait). He has described over a dozen new species and published more than ninety peer-reviewed papers. He grew up in New York City, and his undergraduate degree is from McGill University in Montreal (the city where he was born), while his PhD is from the University of Michigan. He is a former Program Director at the National Science Foundation, an elected fellow of the American Association for the Advancement of Science, and a TED Senior Fellow. He teaches Evolution and Ichthyology at LSU and has given seminars about his work across the country and internationally. He was recently (2020–2021) a Fulbright Distinguished Chair in Environmental Science at Carleton University in Ottawa. He is a father of ten-year-old twins and has been married to his wife Annemarie for seventeen years. He loves them a lot but thought dedicating this book to them would be a bit much.

You can follow him on Twitter @PREAUX_FISH or his Facebook page ‘Dr. Prosanta Chakrabarty’.

Acknowledgments

Penguin Random House Executive Editor, Premanka Goswami, made this book possible and gave me the kind of encouragement that I had always hoped to find in an editor. Ethan Kocak beautifully illustrated the Darwin ‘movie’, ‘From So Simple a Beginning’, in the middle of this book; he is awesome. I must thank LSU, my employer, for the freedom to write what I think and for a job to do all the things I love anyway.

The people at TED gave me the opportunity and confidence to speak on this topic and the platform to be seen; the TED Fellows team is especially amazing (thanks Shoham Arad, Patrick D’Arcy, Tom Rielly and others, past and present, on that squad). I want to thank publicly available information on Wikipedia, Google (especially Google Scholar), the public libraries and the staff at the LSU libraries. Many thanks also to Alexandra Elbakyan for making many scientific publications available to those without means. Mary Jane West-Eberhard, Doug Futuyma, Morgan Kelly, Jeremy Yoder and others all provided helpful comments on various drafts—any remaining mistakes are obviously on them (just kidding!). I suppose I should thank the coronavirus SARS-CoV-2, as it helped me realize how little people understood about infections, transmission and mutation; thanks COVID-19—you suck.

My 2020–2021 pandemic time was largely spent in Ottawa working remotely for LSU and as a Visiting Fulbright Scholar at Carleton University; I must thank them for the opportunity to work safely with my family. The Cooke lab really took me under their wing. Leslie Rissler of the National Science Foundation told me I should write an evolution book, so I did: thanks Leslie.

Lastly I need to thank my family: my wife for helping spread our genes and to our children for carrying them but also for their love and support. I can accomplish little without my family. We had foster kids with us for much of our time during this pandemic, and despite the chaos, they helped me think about the world very differently and with greater appreciation than I was capable of without them. (If you have privilege and resources, please consider helping a child in need.) Chitta and Anurupa Chakrabarty are who gave me life and taught me about life, so I could not write this book about life without those insights—thanks mom and dad, I love you more than is required by evolution.

THE BEGINNING

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This collection published 2022

Copyright © Prosanta Chakrabarty 2022

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Jacket images © Akangksha Sarmah

This digital edition published in 2022.

e-ISBN: 978-9-35492-432-3

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