A machine for language? Certainly, say the neurophysiologists, busy studying the language specializations of the human brain and trying to identify their evolutionary antecedents. Linguists such as Noam Chomsky talk about machinelike "modules" in the brain for syntax, arguing that language is more an instinct (a complex behavior triggered by simple environmental stimuli) than an acquired skill like riding a bicycle.

But structured language presents the same evolutionary problems as feathered forelimbs for flight: you need a lot of specializations to fly even a little bit. How do you get them, if evolution has no foresight and the intermediate stages do not have intermediate payoffs? Some say that the Darwinian scheme for gradual species self-improvement cannot explain our most valued human capability, the one that sets us so far above the apes, language itself.

William Calvin and Derek Bickerton suggest that other evolutionary developments, not directly related to language, allowed language to evolve in a way that eventually promoted a Chomskian syntax. They compare these intermediate behaviors to the curb-cuts originally intended for wheelchair users. Their usefulness was soon discovered by users of strollers, shopping carts, rollerblades, and so on. The authors argue that reciprocal altruism and ballistic movement planning were "curb-cuts" that indirectly promoted the formation of structured language. Written in the form of a dialogue set in Bellagio, Italy, Lingua ex Machina presents an engaging challenge to those who view the human capacity for language as a winner-take-all war between Chomsky and Darwin.

Over the last four decades, most of the significant contributions to the study of language origins and evolution have come from outside the field of linguistics, which has been dominated by theories of transformational-generative grammar. As articulated by Noam Chomsky, these theories generally agree that the ability to learn and use language is innate and specific to humans; they mostly sidestep the issue of how this ability came to be, preferring to treat it as a given of the human mind.

But, neurophysiologist William Calvin and linguist Derek Bickerton observe in this lively book, language is probably not a deus ex machina invention "tacked onto an ape brain." Instead, it evolved, along with the brain, to accommodate an ever more complex social calculus. The authors suggest that this evolution had two major phases. The first ushered in "protolanguage," individual words with only a rudimentary syntax, while the second brought forth a more complicated syntax that allowed the conception and utterance of antitruths, conditionals, and outright falsehoods. Bickerton writes that "it's words, not sentences, that dramatically distinguish our species from others," while Calvin takes a more pointed interest in neural adaptations that allowed for "structured language"--that is, long statements with embedded clauses and phrases. Their account of human language's origins and development does not reject Chomskyan views of language out of hand, as so many scholars have tried to do. Instead, it attempts to forge a reconciliation of notions of innate structure with those of natural selection.

That's a tall order, and, although their book advances some controversial ideas about the relative importance of social intelligence in language formation, Calvin and Bickerton make a fine and comprehensible effort in its pages. --Gregory McNamee