The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution by Richard Dawkins. Houghton Mifflin, $28, 673 pages.


The News & Observer

January 9, 2005

Darwin and Chaucer hook up

By PHILLIP MANNING

Geoffrey Chaucer and Charles Darwin would seem the strangest of bedfellows. But the distinguished British science writer, Richard Dawkins, couples the 14th century poet and the 19th century naturalist to produce a deeply imagined work on the evolutionary history of mankind.

“The Ancestor’s Tale” loosely follows the structure of Chaucer's "Canterbury Tales," except that Dawkins, a professor of the Public Understanding of Science at Oxford University, takes us back in time on an evolutionary pilgrimage to the beginning of life on Earth rather than a journey to the shrine of Thomas à Becket. At 40 different rendezvous points we hook up with our last common ancestors. At rendezvous 1, which occurred about 6 million years ago, we are joined in our trip by our closest living relatives, the chimpanzees. Rendezvous 2 unites the chimps and us with the gorillas. The trip continues until all living things come together at the origin of life.

Along the way, we encounter some truly unusual creatures. Consider, for example, the hagfish, which join our pilgrimage at Rendezvous 22, about 430 million years ago. Hagfish are jawless, limbless, boneless creatures that live at the bottom of the sea. Their spines are cartilage, and their mouths are mere holes, resembling the sucker on an octopus's arm. Hagfish are exceedingly slimy, so slimy in fact that they must literally tie themselves into knots to get a purchase while burrowing into dead fish or whales. Then, they eat their quarry from the inside out. It's not an easy life, but these buzzards of the sea perform the important function of cleaning the ocean floors of carcasses. And it's disconcerting to discover that hagfish are, like us, vertebrates, cousins that share many similar genes.

But Dawkins's book is more than just a curiosity shop. His overriding purpose, not revealed until the last chapter, is to shed light on the nature of evolution itself. To prepare us for his conclusions, Dawkins delves into some aspect of evolutionary science in the tales of almost every creature we meet. The DNA sequences that allow scientists to determine how closely living creatures are related to one another is brilliantly illuminated in the Gibbon's Tale. Dawkins employs an analogy that shows how scholars tracked down the relationships between 85 ancient, hand-copied "Canterbury Tales" manuscripts, each different from the others. Chaucer's original text has been lost, but an examination of the differences between the copies reveals the order of copying.

DNA makes copying errors, too, and those that are beneficial or neutral to the organism are passed from generation to generation. The genetic code that makes us what we are is written in the DNA alphabet - A, G, C, and T. And an analysis of changes in the arrangement of those letters in living organisms yields a family tree of relationships similar to those produced by scholars studying manuscripts of the "Canterbury Tales." Scientists use these DNA trees to establish relationships among plants and animals.

Sometimes the DNA evidence contradicts common sense. For example, zoologists have long classified hippos as pigs. This makes sense, they look like overgrown pigs and act like pigs that took to water. DNA analysis, however, tells a different tale: the hippos' closest living relatives are whales, which resemble hippos hardly at all.

Dawkins livens his science with wit and snatches of doggerel. He explains how natural selection led some birds to lose their wings when they ended up on islands without predators. Of course, when predators do arrive the flightless birds are disadvantaged. When the Maoris reached New Zealand (or Aotearoa, as they called it), the giant, flightless moa found itself in trouble. The Maoris hunted them to extinction for their oversized drumsticks. Dawkins sums up their plight with a verse. "No moa,no moa/In old Ao-tea-roa./Can't get 'em./They've et' em;/ They've gone and there ain't no moa!" This is Dawkins at his best, making science clear, making it fun.

But Dawkins is after bigger game than merely recounting disparate stories of evolution at work. Evolution occurs because of random changes in the DNA of organisms. If a new DNA configuration enables an organism to survive and outreproduce other members of its species, then, after many generations, the new configuration will replace the old one. This process - natural selection - is nonrandom. So, the question Dawkins raises is, Does the combination of random and nonrandom changes, produce a direction to evolution?

Survival, according to the late Stephen Jay Gould, is mostly a matter of luck. Good genes won't help you if a meteor slams into your neighborhood or the climate changes. Gould writes of a thought experiment he calls "replaying life's tape." "[G]o back to any time and place in the past .... Then let the tape run again and see if the repetition looks at all like the original." Gould suspects that each replay would yield a different set of survivors and a "radically different history." Thus, evolution has no direction and does not progress.

Dawkins disagrees. He declares that evolution does "progress in
directions that are at least predictable enough to justify the notion." Dawkins does not mean that natural selection was preordained to produce humans. He proposes only that certain complex adaptations, such as eyes, suggest a version of progress. Owl eyes, for instance, are quite different from fish eyes and evolved independently from them. In fact, Dawkins points out, eyes evolved independently many times in the animal kingdom, so it seems likely that when we replay the tape of life we will get creatures with eyes. Other features, such as venomous stingers and echolocation, also evolved independently more than once, which suggests that a rerun of life would produce similar features. Convergent evolution — the development of similar body plans in unrelated species, such as the remarkable resemblance of marsupials in Australia to placental mammals on other continents — further supports the idea that life might evolve into forms we would recognize if life's tape could be replayed.

The direction of evolution (or the lack of it) is a hotly debated topic among evolutionary scientists, but it seems to me that Mark Twain (as quoted by Dawkins) may have gotten it right: "History doesn't repeat itself, but it rhymes."
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