Free Press. 470 pp. $30

Reviewed by John Horgan

Dawkins calls this work his "missing link." His previous nine books offered reinterpretations of evolutionary theory (The Selfish Gene, The Extended Phenotype) and addressed challenges to it (The Blind Watchmaker, Climbing Mount Improbable). But he never presented the basic evidence for evolution and its prime mover, natural selection. Greatest Show fills that gap in a timely fashion, coming 200 years after Darwin's birth and 150 years after the publication of On the Origin of Species.

Justifying the book, Dawkins deplores the stubborn rejection of evolution by as many as 40 percent of Americans and, he claims, growing numbers of Europeans. He realizes that these nonbelievers, whom he equates with Holocaust deniers, are unlikely to read anything he writes. He hopes that Greatest Show will be absorbed, rather, by those who know evolution deniers, "perhaps members of their own family and church," and want to be "prepared to argue the case."

Dawkins assembles heaps of evidence, packaged as responses to common creationist complaints. What about all those supposedly yawning gaps in the fossil record? They have filled in quite nicely since Darwin's day, especially when it comes to our own ancestry. In reverse chronological order, we now have the archaic forms of Homo sapiens, including Homo sapiens Neanderthalis, then Homo erectus, Homo habilis, and Australopithecus. Dawkins must be thrilled at the recent discovery of yet another missing link, Ardipithecus ramidus, "Ardi," a lovely African lass who lived 4.4 million years ago.

Our bodies bear further witness to our evolutionary past. All mammals share the same basic skeletal pattern, although different bones have different shapes and functions. The nail on your middle finger, Dawkins elaborates, corresponds to the hoof of a horse's foreleg. This relatedness, or "homology," makes no sense if all mammalian species were created de novo by God but makes perfect sense if we all sprang from the same root.

Creationists express incredulity that life could evolve within a mere few billion years from single cells to creatures as complex as manatees and televangelists without divine assistance. And yet every person on the planet, Dawkins points out, grew from a single fertilized cell into a human being in a mere nine months. This process may seem miraculous to the ignorant, but scientists have shown that an embryo unfolds - or, to be more precise, folds and refolds - according to a process that Dawkins, a master of minting new terms, calls "auto-origami." No top-down "architect's plan" guides embryonic development, Dawkins emphasizes, reiterating a favorite theme, but only chemical and physical rules that are "local, local, local."

For those who demand eye-witness evidence of evolution, Dawkins offers the research of the biologist Richard Lenski of Michigan State University, who has bred common gut-dwelling bacteria E. coli with radically different genomes and properties. Some strains are double the size of their ancestors; others can metabolize glucose much more efficiently, and still others can consume citrate, related to the chemical that makes lemons sour.

Dawkins also refutes the tired claim that evolutionary theory, because it concerns the past, makes no predictions and hence is not a "real" scientific theory. In 1862 Darwin himself predicted - based on his recognition of the evolved codependence of many species - that a Madagascar orchid that secretes nectar at the bottom of a foot-long tube must be pollinated by a moth with an equally long proboscis. The moth was discovered in 1903 and dubbed Xanthopan morgani praedicta, with the praedicta a nod to Darwin's prescience.

Dawkins falters only in his wrap-up. Echoing the closing of On the Origin of Species, he asks, "How is it that we find ourselves not merely existing but surrounded by such complexity, such elegance, such endless forms most beautiful and wonderful?" He answers, "It could not have been otherwise, given that we are capable of noticing our existence at all, and of asking questions about it."

Instead of being stirred by this coda, I scribbled, "Oh no!" in the margin. Although he does not use the term anthropic principle, Dawkins comes perilously close to invoking that notorious concept, which some benighted physicists have proposed as a solution to the mystery of the universe. The principle states that that universe must be as we observe it to be, because, if it weren't, we wouldn't be here to observe it.

If this sounds like a tautology, a circular and hence vacuous pseudo-explanation, that's because it is. The anthropic principle is less a theory than an admission of defeat. In spite of the immense explanatory power of modern evolutionary theory, Dawkins is implicitly conceding, life somehow remains as mysterious as ever. If I believed in God, I would thank him for that, too.