You Are Here
A review of The Ancestor's Tale, by Richard Dawkins
I once attended a conference about systematics -- the classification of species -- and felt as if I were looking at Mount Rushmore with a magnifying glass. The names alone -- Tetraconata, Amoebozoa, Ecdysozoa, Oomycota, Neomeniomorpha -- were overwhelming. Speaker after speaker hypothesized about how various species were related -- whether springtails or bristletails were the closest relatives of winged insects, whether sponges all descended from a common ancestor, whether slime molds are really molds. I stumbled out of the lecture hall desperate for the big picture. And suddenly I saw it, on a five-foot-square poster taped to a wall.
It showed an evolutionary tree by David Hillis of the University of Texas and his colleagues. The tree displayed the relationships of 3,000 species of animals, plants, fungi and microbes. The scientists drew it as a kind of a surreal bicycle wheel, each species represented as a tip of a branch along its rim. As my eye moved toward the center of the tree, I moved back through time, our own branch joining together with that of chimpanzees, our closest living relatives. Farther in, all living mammals merged into a common ancestor, and then all vertebrates, and then all animals. The deepest branches of the tree met at the very center, which represented the common ancestor of all living things. Hillis's tree included only a sampling of life's diversity, which has been estimated at 10 million to 100 million species. Yet its tiny branch tips were so densely packed that it was hard to find our own. Fortunately, the poster included a big arrow pointing to Homo sapiens, reading: ''You are here.''
The tree of life was Darwin's greatest and most dislocating discovery. Our species is not the center of nature; it is one among millions of branches, its ancestry mingled with that of pufferfish and puffballs. Yet outside of systematics circles, few people understand how scientists assemble the tree of life, or use it to learn how life has evolved. In ''The Ancestor's Tale,'' the Oxford University zoologist Richard Dawkins offers a tour through the tree's thickety depths. Dawkins, the author of the scientific classics ''The Selfish Gene'' and ''The Blind Watchmaker,'' is an excellent guide, both a profoundly original scientific thinker and a marvelously adept explainer.
He organizes ''The Ancestor's Tale'' as a pilgrimage, leading readers from the tip of our own branch down to the base of the tree of life. He moves back through time, stopping occasionally so we humans can be joined by related species -- first by chimpanzees, which share a common ancestor with us six million to seven million years ago, then by gorillas, orangutans, gibbons, Old World monkeys and so on. Dawkins patterns his book on ''The Canterbury Tales'' of Chaucer, breaking it up into ''The Marsupial Mole's Tale,'' ''The Elephant Bird's Tale'' and many others. In each tale he looks at an aspect of the tree of life or at evolution in general.
Together, the tales add up to an encyclopedia that sheds light on some of the stranger features of the tree of life. For example, it is tempting to look at the platypus, a duck-billed mammal that lays eggs, as a living fossil trapped in the past. In fact, the platypus is no more primitive than we are. True, its ancestors branched off from our own some 180 million years ago, before our more recent ancestors evolved placentas and live births. But the ancestors of today's platypuses were not frozen in time. They evolved sophisticated adaptations of their own, like sense organs in their bills that can detect faint electric fields produced by other animals. From this perspective, it is humans who are the living fossils. Dawkins not only makes an important point here, but does it with flair. He eloquently describes how platypuses combine information from electric-sense organs with signals from mechanical sensors in their bills, likening the process to our measuring how far away a lightning bolt strikes by comparing the flash to the thunder. ''When you think of a platypus, forget duck,'' he writes. ''Think huge hand feeling its way, by remote pins and needles; think lightning flash and thunder rumbling, through the watery mud of Australia.''
As enlightening as ''The Ancestor's Tale'' is, it could have been better. Dawkins clearly wanted it to be more literary, evocative and personal than his previous books. But his efforts are often awkward and halfhearted, as when he writes about earthworms. ''I am privileged to have seen giant earthworms (Megascolides australis), in Australia, said to be capable of growing to four meters long,'' he announces. Cool, the reader thinks -- let's hear what that was like. But Dawkins abruptly abandons earthworms altogether.
The structure of ''The Ancestor's Tale'' could have been better as well. The backward pilgrimage is a brilliant inspiration, which allows Dawkins to ease us into our kinship with the rest of life. Neanderthals come early in the book because of all other species they were our closest relatives. It's not too much of a stretch to see a bond in Neanderthals because they look so much like us. A jellyfish, on the other hand, doesn't exactly seem like family. In part, that's because the common ancestor of jellyfish and humans lived perhaps a billion years ago. But Dawkins introduces us to jellyfish only deep in the book, after we've met many closer relatives.
At the same time, though, the book is wildly lopsided. Dawkins spends nearly 500 pages on animals, and 100 on all other life forms. Fungi, estimated to total 1.5 million species, get four pages. The vast bulk of life, whether measured by sheer biomass or by genetic diversity, lies outside the animal kingdom. And not all the lessons about evolution that the animal kingdom offers apply outside its borders. While animals generally evolve into new species when populations become isolated, plants can also form a new species when two existing species interbreed. Fungi are even weirder. They can form vast subterranean networks of threadlike growths, which sometimes fuse with other networks, mingling their DNA so that they wind up as strange genetic chimeras, defying our notion of what it means to be a genetically distinct individual. Bacteria and other microbes are even more casual with their genes, trading them like baseball cards.
Evolution not only has a different flavor outside the animal kingdom; it also may give the tree of life a different shape. Some scientists today argue that early life did not follow the regular branching pattern of evolution seen in animals. Instead of a tree, a better metaphor might be a ring or a web. These are some of the most important, most fascinating lines of research in evolutionary biology, but Dawkins skims over them.
Despite these shortcomings, this is an ambitious, important book rich with fascinating insights. Also, it couldn't come at a better time. Evolutionary trees have become the lingua franca of biology. Virus hunters draw them to find the origin of SARS and H.I.V. Conservation biologists draw them to decide which endangered species are in most urgent need of saving. Geneticists draw them to pinpoint the genes that have made us uniquely humans. Genome sequencers draw them to discover new genes that may lead to new technologies and medical treatments. If you want to understand these trees -- and through them, the nature of life -- ''The Ancestor's Tale'' is an excellent place to start.
Copyright 2004 The New York Times