Unnatural Selection : ORIGINS RECONSIDERED <i> By Richard Leakey and Roger Lewin</i> , <i> (Doubleday: $25; 375 pp.)</i>

My friend Richard Leakey once appeared in a Rolex-watch ad (not a bad freebie in undoubted recompense). The ad’s text summarized the essence of Leakey’s work in a fine and incisive epitome: “Human evolution was commonly considered an unbroken cord; his studies reveal more complex lines of descent.” Right next to this text, and completely contradicting the accurate words, stands a picture of the conventional ladder-like “march of progress” from stooped ape to upright white male in a business suit. I made a slide of this ad and use it in nearly all my talks to illustrate the continuing influence that myths of linear and predictable progress impose upon our view of human evolution.

Leakey has again teamed up with Roger Lewin, one of our best science writers and an expert in anthropology in his own right, to produce this part-sequel, part-novel follow-up to their best-selling “Origins” of some 15 years ago. The first section, Leakey’s description (through Lewin’s prose) of his most recent African discoveries, is a successful, even riveting, contribution to the growing genre of honest first-person accounts displaying the human face of science (a tradition begun by Jim Watson’s “The Double Helix” in the late 1960s).

We receive a concise review of past work, followed by a closer description of Leakey’s two latest triumphs--discoveries of the “Turkana Boy” (the nearly complete skeleton of Homo erectus, the species immediately ancestral to us), and the “Black Skull” (evidence for yet another hominid lineage from the crucial time of some 2.5 million years ago and indicating, in Leakey’s view, that at least four species of hominids, including our probable ancestor Homo habilis, lived during this interval). As Leakey states in the best tradition of understatement from his British ancestry (though he is a native Kenyan): “Our family tree was getting bushier and bushier, and the West Turkana expeditions had played a major role in its growth. I was very satisfied with that.”

The second part presents Leakey’s perspective on how the fossil record can help us to understand the evolutionary basis of our humanness. He states as his credo: “If this sense of humanity came into being in the course of evolutionary history, then it must have component parts, and they in turn must be identifiable. It is my conviction that we are beginning to identify these components, that we can see the gradual emergence of humanness in our evolutionary history.” No paleontologist (I am one, and I have worked in the field with Richard Leakey) could disagree with this hope, but we must also acknowledge that much of such evident importance--from actions of behavior to the emergence of language--either does not fossilize or emerges from evidence of anatomy only by tenuous and tortuous chains of doubtful inferences. Humility and tentativeness must therefore reign.

I agree with most of Leakey’s scenario for human evolution, but wish that he had been more adventurous in exploring unconventional (but intellectually powerful and, in my view, probably correct) alternatives to the comfortable Darwinian view that all central features of our humanity arose by continuous adaptive improvement from less complicated representations of the same structure or function in ancestors. I would challenge both of these claims (based, as they are, only on convention, and not on evidence), and would propose a more jerky and quirky route to our current and dangerous success.

On continuity, for example, Leakey argues that language evolved as an “extension of vocal abilities” present in the gesturing, signaling and communicating systems of our apelike ancestors. This sounds “obvious” and correct, but may well be wrong under Noam Chomsky’s notion of universal grammar as a unique cognitive module. Language evolved from something simpler, to be sure, but not necessarily from vocal communication systems (sign languages of the deaf have all the richness and complexity of any spoken tongue). Perhaps language evolved as a side-consequence of some other cerebral function, and then co-opted (for its expression) a vocal system that had existed for other reasons.

Similarly, Leakey holds that fundamental features like consciousness must be explicitly evolved by natural selection for immediate utility. He writes: “It is necessary to view consciousness as we view other aspects of ourselves: the direct product of natural selection. In that case, we have to ask what selective benefit consciousness conferred on our ancestors and on us.” Again, this sounds right and obvious at first, yet devolves into difficulty at closer scrutiny. Most of what we call consciousness may well emerge as a byproduct of building powerful brain-computers for other reasons. After all, our brains did not enlarge so that we could read or write, yet these activities are now focal to our success.

Finally, I must raise, gently I trust, a question about mode of composition. I maintain a minor sidelight as a baseball writer and am well familiar with the genre of “as told to” books--pitchers or sluggers teaming with sportswriters who shape their extensive interviews into a first-person text. The art of this genre lies in preserving the distinctive voice of the primary subject--the sports heroes themselves. This book is written entirely in the first person--Leakey’s rather than Lewin’s (and Richard’s name is three times as high as Roger’s on the jacket). Thus, we are to assume (by the “as told to” convention) that we are hearing Richard Leakey’s voice as recorded and arranged by Roger Lewin.

But now we encounter the problem of their departure from the genre’s convention. And what else could they do, for Roger Lewin is also an expert with his own views. I don’t doubt that Richard vetted all Roger’s material, and that everything herein has his approbation and agreement. But I also know that much placed into Richard’s first-person voice has other sources, presumably Roger’s own research and reading.

For example, I read on Page 348 that “we are a contingent fact of history, not an inevitability,” followed by several paragraphs on extinction of dinosaurs as a prerequisite to mammalian dominance. Now I couldn’t possibly agree more--for these lines are from my writing (“Wonderful Life” and several of my essays), not from Richard’s head. (Honest folks, I’m not complaining and couldn’t be more flattered; every scholar seeks this special brand of persistence above all--to have one’s words pass anonymously into general knowledge). And when I read on Page 356 that “in our recent history, two intellectual revolutions shook humanity’s perception of itself. The first was the Copernican revolution. . . . The second was the Darwinian revolution”--well, I recognize this (for I have cited the line so many times) as Freud’s most famous aphorism about the history of science.

I admire Richard Leakey too much as a unique, powerful and brilliant individual to see his voice slip into this consensus format. And I am so fond of Roger Lewin’s writing and insights that I would rather read them under a single masthead three times higher.