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.