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, 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 in a different way 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 their 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 past 10,000 years").

Sadly, anti-evolutionism, 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 2,000 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 for 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 Galápagos 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 must 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.

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