A review by: WILLIAM H. CALVIN

The Co-Evolution of Language and the Brain.
By Terrence W. Deacon.
Illustrated. 527 pp. New York:
W. W. Norton & Company. $29.95.

Our brains are well suited for language. But how did they get that way?

In our evolutionary ascent from an apelike ancestor, we gained our most prized possession, the mental abilities underlying language. We're still trying to figure out what language is (from monkey cries up to structured syntax), how it works (the short-term processes in the brain that construct and deconstruct utterances) and why it evolved. That's what Terrence W. Deacon's book, ''The Symbolic Species,'' is about. His first section is on symbols and language, the next tackles the brain's language specializations and the last addresses the coevolution of language and the human brain, ending up with Darwinian views of consciousness. It is a work of enormous breadth, likely to pleasantly surprise both general readers and experts.

Deacon's first illustration shows four cartoon views of the theories used to explain language: the common-sense view, B. F. Skinner's associations, Noam Chomsky's innate grammatical knowledge and the ''mentalese'' instincts that Steven Pinker describes. Though I am agnostic on what terms to use, I have no doubt that human infants come with an enormous ''acquisitiveness'' for discovering patterns -- and this helps them to zero in on any dialect. Newborns detect typical speech sounds; pretty soon, atypical sounds are forced into a standard category the infant creates. A six-month-old Japanese infant can still detect English ''r'' and ''l'' sounds. But after another six months of exposure to the Japanese phoneme that lies between them (and not to English phonemes), the child standardizes on the Japanese phoneme and hears ''l'' and ''r'' as the same. In English, infants form a few dozen phonemes, but some languages use only a dozen, others up to 141. And they start picking up the common bundles of phonemes: during preschool years, they average six new words a day.

Between 18 and 36 months, children analyze longer patterns of words they hear -- and they discover rules. In English, they'll figure out the ''add -s'' rule for plurals and ''add -ed'' for past tense. They're soon fitting one sentence inside another: ''I think I saw him leave to go home'' has four verbs, and ''This is the house that Jack built'' carries nested embedding to extremes.

To judge from how demanding children become about bedtime stories, they've detected far longer patterns involving many sentences, like Aristotle's rule that all good stories have a distinct beginning, middle and end. This pattern hunger doesn't require even average intelligence, nor is it limited to speech. Deaf children can do the same levels of pattern discovery by observing body movements if they are immersed in a fluent sign-language environment equally early in life. Nothing like this obsession with extracting hidden patterns is seen in other animals. Some pattern-hungry children even go on to become scientists, trying to guess the larger obscure patterns that tell us how the world works and where we came from.

Many types of scientists are attracted by the problem of how fancy language was fitted into an ape brain. But in our search for pattern, we've often been like the blind men examining the elephant. Chomsky, for example, declares that humans have a ''language organ,'' but he doesn't seem to be interested in the evolution, anthropology or neurology of it. You'd think it was some sort of supercharger, tacked onto a conventional engine by a hopeful monster mutation -- and that raises skeptical eyebrows. As Deacon says: ''Innate Universal Grammar . . . is a cure that is more drastic than the disease. It makes sweeping assumptions about brains and evolution that are no less credible than the claim that children are superintelligent learners.''

Many of us assume that any real piecing together of the big story of language evolution is going to come from people acquainted with more than one leg of the elephant, who can combine the perspectives of cognitive neurosciences, anthropology, primatology, linguistics and developmental and evolutionary biology. And that describes Deacon pretty well. He's known as a biological anthropologist at Boston University and a neuroscientist at Harvard Medical School, accustomed to grounding his thinking in known anatomy and physiology. He's at home all across the relevant territory. If you've been reading Pinker, Derek Bickerton, Daniel Dennett, Merlin Donald, Ray Jackendoff, Melvin Konner, Philip Lieberman or Sue Savage-Rumbaugh, then you are surely going to want to read Deacon's lovely book.

Evolutionary explanations for language and brain enlargement are often offered up in an overly simplistic way that gives Darwinian endeavors a bad name. Deacon neatly avoids this by showing how flexibility during life (learning and creativity) eventually helps to reward genetic variations leading in a similar functional direction. This form-follows-function principle, called the Baldwin effect, has been known for a century, but it's still poorly appreciated. Since it is correct but unintuitive, let me illustrate it here through recipes: Anyone asking for a copy of a recipe ought to realize the donor has long since stopped consulting it; he or she just improvises from memory and, over the years, has improved the cake considerably. Still, the original version is what's copied, usually with some unintentional mutations (you confuse teaspoons with tablespoons, or transcribe temperatures incorrectly). Most errors are bad news -- but no one asks for copies of those next-generation recipes, only the ones whose errors came closer to the master chef's actual practice. This dropout creates a slow convergence in copying errors toward written recipes with a combination of ingredients, amounts, times, temperatures and procedures that -- with common-sense tweaking -- will satisfy ''good taste.''

The Baldwin effect allows unrecorded tweaking from flexible behavior to secondarily drag along relevant genes (recipe items) in the long run; it's Darwinian, but at one remove. Thus relevant gene combinations ''fill in'' behind the behavioral advance. Deacon makes good use of this anatomy-follows-behavior principle in addressing tool making by larger-brained Homo species that evolved from the Australopithecines with ape-sized brains: ''The Baldwinian perspective suggests . . . that the first stone tools were manufactured by Australopithecines, and that the transition into Homo was in part a consequence rather than the cause. . . . The large brains, stone tools, reduction in dentition, better opposability of thumb and fingers, and more complete bipedality found in post-australopithecine hominids are the physical echoes of a threshold already crossed'' in behavior. ''Ultimately, all these curious physical traits that distinguish modern human bodies and brains were caused by ideas shared down the generations.''

Deacon next discusses what aspects of language could have become established through Darwinian means during hominid evolution, after first being carried along culturally. He makes the usual mistake: being overly specific. ''If symbolic communication did not arise due to a 'hopeful monster' mutation of the brain, it must have been selected for.'' But selection that favors language need not come from the success of language per se. For example, some brain circuitry is shared between planning complex hand and arm movements and complex language. Variants promoting successful hammering and throwing may also aid language ability -- and vice versa.

Deacon's deep knowledge of anthropology is evident in his analysis of the development 2.5 million years ago of reproductive strategies involving hunting and the provisioning of mates and offspring: ''Symbolic culture was a response to a reproductive problem that only symbols could solve: the imperative of representing a social contract.'' This involves exclusive mating: human adultery is more than animal philandery or desertion; ''it involves betrayal,'' he writes, adding that there can be no betrayal without implicit promises.

It also involves ''But you owe me!'' The benefits of reciprocal altruism require that freeloading be minimized, and, as the linguist Derek Bickerton recently noted, the nonlanguage task of remembering who owes what to whom sets us up to understand structured sentences. They carry over into linguistic argument structures (the word categories involving actors, recipients, beneficiaries) that provide major clues to understanding a sentence about who did what to whom.

The exacting methods of Deacon's lab work on embryonic brain tissue are reflected in the way he frames sociobiological questions. He avoids the jargon (''Language Acquisition Device, or LAD'') often created by cognitive cognoscenti trying to define their way into the unknown. Deacon's grounding in biological ideas gives his well-focused book an entirely different flavor from many books on language origins, with a lot to chew on. Some will find this threatening, others refreshing.

William H. Calvin is a theoretical neurophysiologist at the University of Washington and the author of "How Brains Think" and "The Cerebral Code."