The Improbability Pump
Imagine for a moment that a large proportion of Americans--let's say half--rejected the "germ theory" of infectious disease. Maladies like swine flu, malaria and AIDS aren't caused by micro-organisms, they claim, but by the displeasure of gods, whom they propitiate by praying, consulting shamans and sacrificing goats. Now, you'd surely find this a national disgrace, for those people would be utterly, unequivocally wrong. Although it's called germ theory, the idea that infections are spread by small creatures is also a fact, supported by mountains of evidence. You don't get malaria unless you carry a specific protozoan parasite. We know how it causes the disease, and we see that when you kill it with drugs, the disease goes away. How, we'd ask, could people ignore all this evidence in favor of baseless superstition?
But that's fiction, right? Well, not entirely, for it applies precisely to another "theory" that is also a fact: the theory of evolution. Over the past quarter-century, poll after poll has revealed that nearly half of all Americans flatly reject evolution, many clinging to the ancient superstition that the earth was created only 6,000 years ago, complete with all existing species. But as Richard Dawkins shows in his splendid new book, The Greatest Show on Earth, the theory of evolution is supported by at least as much evidence as is the germ theory of disease--heaps of it, and from many areas of biology. So why is it contemptible to reject germ theory but socially acceptable to reject evolutionary theory?
One answer is religion. Unlike germ theory, the idea of evolution strikes at the heart of human ego, suggesting that we were not the special object of God's attention but were made by the same blind and mindless process of natural selection that also built ferns, fish and rabbits. Another answer is ignorance: most Americans are simply unaware of the multifarious evidence that makes evolution more than "just a theory," and don't even realize that a scientific theory is far more than idle speculation.
While Dawkins has produced several brilliant books on the marvels of evolution and natural selection, he's never before written at length about the evidence for evolution. The Greatest Show on Earth can be seen as his response to ongoing and nonscientific opposition to evolution. In his previous book, The God Delusion, Dawkins mounted a withering attack on belief that was surely motivated in part by his incessant battles with faith-based creationism. In The Greatest Show on Earth he finally addresses the problem of ignorance, drawing together the diverse evidence for evolution to show that "evolution is a fact. Beyond reasonable doubt, beyond serious doubt, beyond sane, informed, intelligent doubt, beyond doubt evolution is a fact." Dawkins has two goals here. The first is to change the minds of those who doubt or deny evolution by presenting them with more than 400 pages of scientific evidence. But changing minds is a big job, at least in the United States: in a 2006 Time magazine poll, 64 percent of Americans declared that if science disproved one of their religious beliefs, they'd reject the science in favor of their faith. (The British aren't quite so defiant: one week after its publication, The Greatest Show on Earth debuted at No. 1 on the Sunday Times bestseller list.) More realistically, Dawkins hopes to bolster those who already accept evolution but "find themselves inadequately prepared to argue the case." And here he succeeds brilliantly.
In contrast, Jerry Fodor and Massimo Piattelli-Palmarini (hereafter "F&P") think the case should be dismissed. In their provocatively titled What Darwin Got Wrong they contend that ever since the 1859 publication of On the Origin of Species, scientists and laymen alike have been bamboozled by Darwin's key idea: natural selection, which F&P see as logically incoherent and lacking in empirical support. Since the authors are neither creationists nor crackpots--Fodor, a respected philosopher of mind, and Piattelli-Palmarini, a cognitive scientist, both accept the fact of evolution--their arguments deserve careful scrutiny. Unfortunately, in the end their critique proves as biologically uninformed as it is strident, and despite their repeated avowals that Darwinism is dead, it refuses to lie down.
Demonstrating the truth of natural selection is just one of Dawkins's aims, for the theory of evolution is composed of several more or less independent parts, which I like to describe in one longish sentence: "Life on earth evolved gradually, beginning with one primitive species; it then branched out over time, throwing off many new and diverse species--and the process producing the illusion of design in organisms is natural selection." This sentence constitutes a scientific theory, which is not just a guess but an informed statement about the general principles that explain many observations about nature.
Establishing that all these principles are true is a tall order, clearly demanding lots of evidence. And for most people, the evidence boils down to one thing: fossils. Although Darwin was faced with a scant fossil record (it played almost no role in his Origin of Species), since 1859 paleontologists have unearthed a wealth of fossils demonstrating not only gradual change of species over time but also the branching of lineages and the so-called "missing links" that connect major groups of animals. We see marine plankton, whose fossil record is superb, changing slowly and gradually, and early horses branching off into numerous descendants (only a few of which survive today). We have transitional fossils between fish and amphibians, mammals and reptiles, whales and their deerlike ancestors, birds and feathered dinosaurs, and, of course, fossils that link Homo sapiens to our cranially challenged ancestors. Evolution, you might say, is written in the rocks.
But as Dawkins points out, "we don't need fossils in order to demonstrate that evolution is a fact. The evidence for evolution would be entirely secure, even if not a single corpse had ever fossilized." What is this other evidence?