Richard Dawkins, the indefatigable English evolutionist and foremost writer on his subject, has issued what may be the longest and most elegant put-down in the history of science writing. “The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution” (Houghton Mifflin, 688 pages, $28) is anything but a one-liner – in fact, it is a tour de force – but in purpose and effect, it maps squarely onto a classic.

To wit: American engineers, designing the control cab for a new high-speed train, worried about damaging collisions between low-flying birds and the locomotive windshield. Learning that British engineers had solved a similar problem in designing the Concorde, they asked for guidance. The Brits sent plans for a large-bore gun to fire dead chickens at a mock-up of the airliner. The Americans built an exact

copy and proceeded to test it. The first shot shattered not only the windshield but the entire mock-up. The dumbfounded engineers studied this disaster and sent a painstaking analysis to their British peers, seeking advice. It came back via e-mail: “Defrost the chicken.”

To the extent that biological science now understands the relationships of descent with modification – and it does so in remarkable detail, considering the difficulties – “The Ancestor’s Tale” sets them forth in plain English. For that alone it should be read by anyone who cares (positively or negatively!) about evolution. Creationist maundering over mathematical probability to “show” that biological things can’t arise “by chance” (nothing has ever evolved “by chance” alone); clumsy renditions of thermodynamics that “refute Darwinism”; nitpickings in the comparative biochemistry of molecular-biological reactions and structures; the claim that the methodological naturalism of science is just another faith – all these are fusillades of frozen fowl.

A truly comprehensive book like “The Ancestor’s Tale,” accessible to the intelligent lay reader, has been badly needed. We have Mr. Dawkins’s book before us now, to read and to judge. Directly or indirectly, the newest knowledge is represented, described, and (to the best of the author’s ability) explained. This reflects not just the contemporary emergence of evolutionary engineering and computer and cognitive sciences, “Darwinian” medicine, and evolutionary psychology, but more important, an internal expansion of evolutionary insight for all biology. It is impossible today to do serious basic or applied research in cell biology, genetics, pharmacology, immunology, pathology, or biochemistry without comparative methods and reference to current knowledge of evolution.

“The Ancestor’s Tale” needed to be a big book, despite its unitary message. Speciation, for example, is one of the fastest-growing sub disciplines of evolution. It tends to be news to non-biologists that this subject can be studied. But species formation has been observed many times, in nature and in experiment, even though in general for multicellular animals it takes a very long time. There are nevertheless abundant means for studying the splitting of one species into two (or more). In “The Ancestor’s Tale,” explanation of the current methods covers a dozen or two pages. For summarizing the state of all current knowledge of the evolution of life, Dawkins needs 688 pages. But: the most recent research monograph on speciation alone (Jerry A. Coyne and H. Allen Orr, “Speciation”), mostly very current theory and data – and sparing of words – fills 520 dense, small-type, illustration-free pages. Mr. Dawkins’s book is a marvel of sagacious compression.

The author’s challenge was not only to tell the story compactly but to keep the reader wide awake, eager to turn the pages. He accomplishes this through an original device: The authorial voice tells the history of life back ward, as a journey, beginning with ourselves, who are joined by successive ancestors as we progress through 4 billion years. The reader proceeds through biological history, joined at appropriate points by cousins of sequentially greater remove. By the end, it seems a Chaucerian pilgrimage or even a Dantean journey downward. The search ends at the last (or first) common ancestor of all things that live.

This is a panoramic portrait of a big science, as solid as any science we have. In places it is difficult material; not, perhaps, as thorny for the non-specialist as quantum gravity or superstring theory, but close enough. The main arguments of modern systematics (biological classification) are a case in point. Graduate students, even the well prepared, need time and effort to understand systematics well enough to join in the work of deducing relationships. In this book, the “why” of proposed conclusions about relationship is treated at length and with sympathy for the reader. It is fundamental to the argument. For the whole argument, and it is an argument, hinges upon the warrant and justification – the quality of evidence – for the relationships in space and time of all those ancestors. There are arguments among the specialists over the application of methods ranging from formal logic through supercomputing to the dating of fossils. But the achieved agreements are central to making a plausible family tree for life.

Telling this vast story in so charming a way is a major accomplishment. More like mere journalism are the book’s very few caesuras for political opinion. These can take the form, for example, of sneers at President Bush. He pronounced nuclear “nucular.” (Have you heard an intellectual, European or otherwise, sneer at Jimmy Carter for having done it?) This sort of thing ought not to be in books meant to last. It interrupts, just momentarily, a graceful exposition. And there is a certitude in these little observations that Mr. Dawkins the vigilant scientist would reject were they about his own subject.

On other questions, such as the reality of “race” among humans, the discussion in this book is informed, extensive, and impartial. There is such a thing as race within the human species; all people recognize it, and we do so despite the visible continuum of racial characteristics. These are no more discrete, at the level of physiology and genetics, than are the “colors” we see; nevertheless, we see subpopulations just as we see colors. The relevant question for students of our species history is how, in evolution, these subpopulations arose and were maintained, and what that means in the modern world, with population shifts and gene flow between subpopulations inexorably on the rise.

Mr. Dawkins’s new book really amounts to this: “Despite niggling complaints, it remains fact that the diversity of life is due to (‘Darwinian’) evolution, whose mechanisms insure descent with modification.” Does that one-liner need nearly 700 pages, and the valuable collaboration in writing parts of it by Mr. Dawkins’s assistant, Yan Wong? Yes, for descent with modification is the leitmotif of all our knowledge about evolution. Do you want to know why there is a fossil record, or how we can assign dates to skeletons turned to stone? Do you wonder whether that record really shows progression of body plans, or doubt that within it there are proper “intermediates?” Would you like to know to what extent the conclusions of paleontology have been tested, confirmed, and expanded by entirely independent methods of chemistry, genetics, developmental biology? Read this book.

Read it with sufficient care to reproduce, perhaps to teach someone else, the basics of biological systematics, taxonomy, and cladistics. Read it well enough to feel confident about understanding why the most-used definition of “species” (Ernst Mayr’s “biological species concept”) is arbitrary but grounded in what can often be tested – reproductive compatibility. Learn that the definitions of all “higher” categories – genera, families, classes, phyla must be just plain arbitrary. They are as arbitrary as calling photons that reach our eyes, vibrating at wavelengths in the middle of the visible spectrum, “green” – arbitrary but still useful, indeed indispensable.

Once you have, you will never again be carried away by emotion, poetry, or sophistry about the history and mind-boggling variety of life on this planet. Far from rendering you cold or indifferent to its awe, its loveliness, and mystery, it will raise your appreciation to levels that can bring respite to a heart beset with the day’s problems.

Mr. Gross is university professor of the life sciences, emeritus, at the University of Virginia.