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Table of Contents

Title Page Copyright Page Dedication Preface Introduction Chapter 1 - What Is Evolution?

Chapter 2 - Written in the Rocks Chapter 3 - Remnants: Vestiges, Embryos, and Bad Design Chapter 4 - The Geography of Life Chapter 5 - The Engine of Evolution Chapter 6 - How Sex Drives Evolution Chapter 7 - The Origin of Species

Chapter 8 - What About Us? Chapter 9 - Evolution Redux Notes Glossary Suggestions for Further Reading References Illustration Credits Index

“A stunning achievement. Coyne has produced a classic —whether you are an expert or novice in science, a friend or foe of evolutionary biology, reading Why Evolution Is True is bound to be an enlightening experience.”

—Neil Shubin, author of Your Inner Fish

“Jerry Coyne has long been one of the world’s most skillful defenders of evolutionary science in the face of religious obscurantism. In Why Evolution Is True, he has produced an indispensable book: the single, accessible volume that makes the case for evolution. But Coyne has

delivered much more than the latest volley in our ‘culture war’; he has given us an utterly fascinating, lucid, and beautifully written account of our place in the natural world. If you want to better understand your kinship with the rest of life, this book is the place to start.”

—Sam Harris, author of The End of Faith and Letter to a Christian Nation, and

founder of the Reason Project

“Evolution is the foundation of modern biology, and in Why Evolution Is True, Jerry Coyne masterfully explains why. From the vast trove of evidence that evolution scientists have gathered, Coyne has carefully selected some of the most striking

examples and explained them with equal parts grace and authority.”

—Carl Zimmer, author of Microcosm: E. coli and the New Science of Life

“Jerry Coyne’s book does an outstanding job making the basic concepts of evolution understandable for the

average reader. He covers topics ranging from the fossil record to biogeography to the genetic mechanisms of evolution with equal clarity, and shows convincingly why creationism and ’intelligent design’ fail miserably as science.”

—Donald R. Prothero, professor of geology at Occidental College, and author of Evolution: What

the Fossils Say and Why It Matters

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Preface

December 20, 2005. Like many scientists on that day, I awoke feeling anxious. John Jones III, a federal judge in Harrisburg, Pennsylvania, was due to issue his ruling in the case of Kitzmiller et al. vs. Dover Area School

District et al. It had been a watershed trial, and Jones’s judgment would decide how American schoolchildren would learn about evolution.

The educational and scientific crisis had begun modestly enough, when administrators of the Dover, Pennsylvania, school district met to discuss which biology textbooks to order for the local high school. Some

religious members of the school board, unhappy with the current text’s adherence to Darwinian evolution, suggested alternative books that included the biblical theory of creationism. After heated wrangling, the board passed a resolution requiring biology teachers at Dover High to read the following statement to their ninth-grade classes:

The Pennsylvania Academic Standards require students to learn about Darwin’s Theory of Evolution and eventually to take a standardized test of which evolution is a part. Because Darwin’s Theory is a theory, it continues to be tested as new evidence is

discovered. The Theory is not a fact. Gaps in the Theory exist for which there is no evidence.... Intelligent design is an explanation of the origin of life that differs from Darwin’s view. The reference book Of Pandas and People is available for students to see if they

would like to explore this view in an effort to gain an understanding of what intelligent design actually involves. As is true with any theory, students are encouraged to keep an open mind.

This ignited an educational firestorm. Two of the nine school board members

resigned, and all the biology teachers refused to read the statement to their classes, protesting that “intelligent design” was religion rather than science. Since offering religious instruction in public schools violates the United States Constitution, eleven outraged parents took the case to court.

The trial began on September 26, 2005, lasting

six weeks. It was a colorful affair, justifiably billed as the “Scopes Trial of our century,” after the famous 1925 trial in which high school teacher John Scopes, from Dayton, Tennessee, was convicted for teaching that humans had evolved. The national press descended on the sleepy town of Dover, much as it had eighty years earlier on the sleepier town of Dayton.

Even Charles Darwin’s great- great-grandson, Matthew Chapman, showed up, researching a book about the trial.

By all accounts it was a rout. The prosecution was canny and well prepared, the defense lackluster. The star scientist testifying for the defense admitted that his definition of “science” was so broad that it could include

astrology. And in the end, Of Pandas and People was shown to be a put-up job, a creationist book in which the word “creation” had simply been replaced by the words “intelligent design.”

But the case was not open and shut. Judge Jones was a George W. Bush appointee, a devoted churchgoer, and a conservative Republican— not exactly pro-Darwinian

credentials. Everyone held their breath and waited nervously.

Five days before Christmas, Judge Jones handed down his decision— in favor of evolution. He didn’t mince words, ruling that the school board’s policy was one of “breathtaking inanity,” that the defendants had lied when claiming they had no religious motivations,

and, most important, that intelligent design was just recycled creationism:

It is our view that a reasonable, objective observer would, after reviewing both the voluminous record in this case, and our narrative, reach the inescapable conclusion that ID is an interesting

theological argument, but that it is not science.... In summary, the [school board’s] disclaimer singles out the theory of evolution for special treatment, misrepresents its status in the scientific community, causes students to doubt its validity without

scientific justification, presents students with a religious alternative masquerading as a scientific theory, directs them to consult a creationist text [Of Pandas and People] as though it were a science resource, and instructs students to forego scientific inquiry in the public

school classroom and instead to seek out religious instruction elsewhere.

Jones also brushed aside the defense’s claim that the theory of evolution was fatally flawed:

To be sure, Darwin’s theory of evolution is imperfect. However, the fact that a

scientific theory cannot yet render an explanation on every point should not be used as a pretext to thrust an untestable alternative hypothesis grounded in religion into the science classroom to misrepresent well- established scientific propositions.

But scientific truth is decided by scientists, not by judges. What Jones had done was simply prevent an established truth from being muddled by biased and dogmatic opponents. Nevertheless, his ruling was a splendid victory for American schoolchildren, for evolution, and, indeed, for science itself.

All the same, it wasn’t a time to gloat. This was

certainly not the last battle we’d have to fight to keep evolution from being censored in the schools. During more than twenty-five years of teaching and defending evolutionary biology, I’ve learned that creationism is like the inflatable roly-poly clown I played with as a child: when you punch it, it briefly goes down, but then pops back up.

And while the Dover trial is an American story, creationism isn’t a uniquely American problem. Creationists—who aren’t necessarily Christians—are establishing footholds in other parts of the world, especially the United Kingdom, Australia, and Turkey. The battle for evolution seems never- ending. And the battle is part

of a wider war, a war between rationality and superstition. What is at stake is nothing less than science itself and all the benefits it offers to society.

The mantra of evolution’s opponents, whether in America or elsewhere, is always the same: “The theory of evolution is in crisis.” The implication is that there are some profound observations

about nature that conflict with Darwinism. But evolution is far more than a “theory,” let alone a theory in crisis. Evolution is a fact. And far from casting doubt on Darwinism, the evidence gathered by scientists over the past century and a half supports it completely, showing that evolution happened, and that it happened largely as Darwin

proposed, through the workings of natural selection.

This book lays out the main lines of evidence for evolution. For those who oppose Darwinism purely as a matter of faith, no amount of evidence will do—theirs is a belief not based on reason. But for the many who find themselves uncertain, or who accept evolution but are not sure how to argue their case,

this volume gives a succinct summary of why modern science recognizes evolution as true. I offer it in the hope that people everywhere may share my wonder at the sheer explanatory power of Darwinian evolution, and may face its implications without fear.

Any book on evolutionary biology is necessarily a collaboration, for the field enfolds areas as diverse as paleontology, molecular biology, population genetics, and biogeography; no one person could ever master them all. I am grateful for the

help and advice of many colleagues who have patiently instructed me and corrected my errors. These include Richard Abbott, Spencer Barrett, Andrew Berry, Deborah Charlesworth, Peter Crane, Mick Ellison, Rob Fleischer, Peter Grant, Matthew Harris, Jim Hopson, David Jablonski, Farish Jenkins, Emily Kay, Philip Kitcher, Rich Lenski, Mark

Norell, Steve Pinker, Trevor Price, Donald Prothero, Steve Pruett-Jones, Bob Richards, Callum Ross, Doug Schemske, Paul Sereno, Neil Shubin, Janice Spofford, Douglas Theobald, Jason Weir, Steve Yanoviak, and Anne Yoder. I apologize to those whose names have been inadvertently omitted, and exculpate all but myself for any remaining errors. I am

especially grateful to Matthew Cobb, Naomi Fein, Hopi Hoekstra, Latha Menon, and Brit Smith, who read and critiqued the entire manuscript. The book would have been substantially poorer without the hard work and artistic acumen of the illustrator, Kalliopi Monoyios. Finally, I am grateful to my agent, John Brockman, who agreed that

people needed to hear the evidence for evolution, and to my editor at Viking Penguin, Wendy Wolf, for her help and support.

Introduction

Darwin matters because evolution matters. Evolution matters because science matters. Science matters because it is the preeminent story of our age, an epic saga about who we are, where we came from, and where we are going.

-Michael Shermer

Among the wonders that science has uncovered about the universe in which we dwell, no subject has caused more fascination and fury than evolution. That is probably because no majestic galaxy or fleeting neutrino has implications that are as

personal. Learning about evolution can transform us in a deep way. It shows us our place in the whole splendid and extraordinary panoply of life. It unites us with every living thing on the earth today and with myriads of creatures long dead. Evolution gives us the true account of our origins, replacing the myths that satisfied us for thousands of years. Some find this

deeply frightening, others ineffably thrilling.

Charles Darwin, of course, belonged to the second group, and expressed the beauty of evolution in the famous final paragraph of the book that started it all—On the Origin of Species (1859):

There is grandeur in this view of life, with its several powers,

having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

But there is even more cause for wonder. For the process of evolution-natural selection, the mechanism that drove the first naked, replicating molecule into the diversity of millions of fossil and living forms—is a mechanism of staggering simplicity and beauty. And only those who understand it can experience the awe that comes with realizing how

such a straightforward process could yield features as diverse as the flower of the orchid, the wing of the bat, and the tail of the peacock. Again in The Origin, Darwin —imbued with Victorian paternalism—described this feeling:

When we no longer look at an organic being as a savage looks at a ship, as

something wholly beyond his comprehension; when we regard every production of nature as one which has had a long history; when we contemplate every complex structure and instinct as the summing up of many contrivances, each useful to the

possessor, in the same way as any great mechanical invention is the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting—I speak from experience

—does the study of natural history become!

Darwin’s theory that all of life was the product of evolution, and that the evolutionary process was driven largely by natural selection, has been called the greatest idea that anyone ever had. But it is more than just a good theory, or even a beautiful one. It also happens

to be true. Although the idea of evolution itself was not original to Darwin, the copious evidence he mustered in its favor convinced most scientists and many educated readers that life had indeed changed over time. This took only about ten years after The Origin was published in 1859. But for many years thereafter, scientists remained skeptical about Darwin’s key

innovation: the theory of natural selection. Indeed, if ever there was a time when Darwinism was “just a theory,” or was “in crisis,” it was the latter half of the nineteenth century, when evidence for the mechanism of evolution was not clear, and the means by which it worked—genetics—was still obscure. This was all sorted out in the first few decades of

the twentieth century, and since then the evidence for both evolution and natural selection has continued to mount, crushing the scientific opposition to Darwinism. While biologists have revealed many phenomena that Darwin never imagined —how to discern evolutionary relationships from DNA sequences, for one thing—the theory presented

in The Origin of Species has, in the main, held up steadfastly. Today scientists have as much confidence in Darwinism as they do in the existence of atoms, or in microorganisms as the cause of infectious disease.

Why then do we need a book that gives the evidence for a theory that long ago became part of mainstream science? After all, nobody

writes books explaining the evidence for atoms, or for the germ theory of disease. What is so different about evolution?

Nothing—and everything. True, evolution is as solidly established as any scientific fact (it is, as we will learn, more than “just a theory”), and scientists need no more convincing. But things are different outside scientific

circles. To many, evolution gnaws at their sense of self. If evolution offers a lesson, it seems to be that we’re not only related to other creatures but, like them, are also the product of blind and impersonal evolutionary forces. If humans are just one of many outcomes of natural selection, maybe we aren’t so special after all. You can understand why this doesn’t

sit well with many people who think that we came into being differently from other species, as the special goal of a divine intention. Does our existence have any purpose or meaning that distinguishes us from other creatures? Evolution is also thought to erode morality. If, after all, we are simply beasts, then why not behave like beasts? What can keep us moral if

we’re nothing more than monkeys with big brains? No other scientific theory produces such angst, or such psychological resistance.

It’s clear that this resistance stems largely from religion. You can find religions without creationism, but you never find creationism without religion. Many religions not only deem humans as special, but deny

evolution by asserting that we, like other species, were objects of an instantaneous creation by a deity. While many religious people have found a way to accommodate evolution with their spiritual beliefs, no such reconciliation is possible if one adheres to the literal truth of a special creation. That is why opposition to evolution is so strong in the United States

and Turkey, where fundamentalist beliefs are pervasive.

Statistics show starkly how resistant we are to accepting the plain scientific fact of evolution. Despite incontrovertible evidence for evolution’s truth, year after year polls show that Americans are depressingly suspicious about this single branch of biology. In 2006,

for example, adults in thirty- two countries were asked to respond to the assertion “Human beings, as we know them, developed from earlier species of animals,” by answering whether they considered it true, false, or were unsure. Now, this statement is flatly true: as we will see, genetic and fossil evidence shows that humans descend from a primate

lineage that split off from our common ancestor with the chimpanzees roughly seven million years ago. And yet only 40 percent of Americans —four in ten people—judge the statement true (down 5 percent from 1985). This figure is nearly matched by the proportion of people who say it’s false: 39 percent. And the rest, 21 percent, are simply unsure.

This becomes even more remarkable when we compare these statistics to those from other Western countries. Of the thirty-one other nations surveyed, only Turkey, rife with religious fundamentalism, ranked lower in accepting evolution (25 percent accept, 75 percent reject). Europeans, on the other hand, score much better, with over 80 percent

of French, Scandinavians, and Icelanders seeing evolution as true. In Japan, 78 percent of people agree that humans evolved. Imagine if America ranked next to last among countries accepting the existence of atoms! People would immediately go to work improving education in the physical sciences.

And evolution gets bumped down even further when it

comes to deciding not whether it’s true, but whether it should be taught in the public schools. Nearly two- thirds of Americans feel that if evolution is taught in the science classroom, creationism should be as well. Only 12 percent—one in eight people—think that evolution should be taught without mentioning a creationist alternative.

Perhaps the “teach all sides” argument appeals to the American sense of fair play, but to an educator it’s truly disheartening. Why teach a discredited, religiously based theory, even one widely believed, alongside a theory so obviously true? It’s like asking that shamanism be taught in medical school alongside Western medicine, or astrology be presented in

psychology class as an alternative theory of human behavior. Perhaps the most frightening statistic is this: despite legal prohibitions, nearly one in eight American high school biology teachers admits to presenting creationism or intelligent design in the classroom as a valid scientific alternative to Darwinism. (This may not be surprising given that one in

six teachers believes that “God created human beings pretty much in their present form within the last 10,000 years.”)

Sadly, antievolutionism, often thought to be a peculiarly American problem, is now spreading to other countries, including Germany and the United Kingdom. In the UK, a 2006 poll by the BBC asked two thousand

people to describe their view of how life formed and developed. While 48 percent accepted the evolutionary view, 39 percent opted for either creationism or intelligent design, and 13 percent didn’t know. More than 40 percent of the respondents thought that either creationism or intelligent design should be taught in school science

classes. That isn’t so different from the statistics from America. And some schools in the UK do present intelligent design as an alternative to evolution, an educational tactic illegal in the United States. With evangelical Christianity gaining a foothold in mainland Europe, and Muslim fundamentalism spreading through the Middle

East, creationism follows in their wake. As I write, Turkish biologists are fighting a rearguard action against well-funded and vociferous creationists in their own country. And—the ultimate irony—creationism has even established a foothold on the Galapagos archipelago. There, on the very land that symbolizes evolution, the iconic islands

that inspired Darwin, a Seventh-day Adventist school dispenses undiluted creationist biology to children of all faiths.

Aside from its conflict with fundamentalist religion, much confusion and misunderstanding surrounds evolution because of a simple lack of awareness of the weight and variety of evidence in its favor.

Doubtless some simply aren’t interested. But the problem is more widespread than this: it’s a lack of information. Even many of my fellow biologists are unacquainted with the many lines of evidence for evolution, and most of my university students, who supposedly learned evolution in high school, come to my courses knowing almost nothing of

this central organizing theory of biology. In spite of the wide coverage of creationism and its recent descendant, intelligent design, the popular press gives almost no background on why scientists accept evolution. No wonder then that many people fall prey to the rhetoric of creationists and their deliberate mischaracterizations of

Darwinism.

Although Darwin was the first to compile evidence for the theory, since his time scientific research has uncovered a stream of new examples showing evolution in action. We are observing species splitting into two, and finding more and more fossils capturing change in the past —dinosaurs that have sprouted feathers, fish that

have grown limbs, reptiles turning into mammals. In this book I weave together the many threads of modern work in genetics, paleontology, geology, molecular biology, anatomy, and development that demonstrate the “indelible stamp” of the processes first proposed by Darwin. We will examine what evolution is, what it is not, and how one tests the

validity of a theory that inflames so many.

We will see that while recognizing the full import of evolution certainly requires a profound shift in thinking, it does not inevitably lead to the dire consequences that creationists always paint when trying to dissuade people from Darwinism. Accepting evolution needn’t turn you into a despairing

nihilist or rob your life of purpose and meaning. It won’t make you immoral, or give you the sentiments of a Stalin or Hitler. Nor need it promote atheism, for enlightened religion has always found a way to accommodate the advances of science. In fact, understanding evolution should surely deepen and enrich our appreciation of the

living world and our place in it. The truth—that we, like lions, redwoods, and frogs, all resulted from the slow replacement of one gene by another, each step conferring a tiny reproductive advantage —is surely more satisfying than the myth that we were suddenly called into being from nothing. As so often happens, Darwin put it best:

When I view all

beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled.

Chapter 1

What Is Evolution?

A curious aspect of the theory of evolution is that everybody thinks he understands it.

—Jacques Monod

If anything is true about nature, it is that plants and animals seem intricately and almost perfectly designed for living their lives. Squids and flatfish change color and

pattern to blend in with their surroundings, becoming invisible to predator and prey. Bats have radar to home in on insects at night. Hummingbirds, which can hover in place and change position in an instant, are far more agile than any human helicopter, and have long tongues to sip nectar lying deep within flowers. And the flowers they visit also appear

designed—to use hummingbirds as sex aids. For while the hummingbird is busy sipping nectar, the flower attaches pollen to its bill, enabling it to fertilize the next flower that the bird visits. Nature resembles a well-oiled machine, with every species an intricate cog or gear.