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In a manner of speaking

For a long time, the main argument against the theory of evolution was the human soul, and the chief evidence for the existence of the soul was language. All humans and only humans have language; therefore humans must have a unique essence, which philosophers and theologians called "soul." "Explain that!" they cried defiantly at scientists. And the scientists couldn't.

On other grounds, however - including geology, which showed that the earth was old enough for very large changes to have occurred very gradually; archeology, which has discovered many of the innumerable links in the skeletal development of humans and other animals; and genetics, which has banished the concept of "essence" from biology - the debate over evolution is now settled. Still, what about language? We know now that language must have an evolutionary explanation, because that is the only kind of explanation there is for any human trait. But what might that explanation be?

Naturally, the answer depends on what language itself is. Until the mid-20th century, the usual answer was that language was just another skill, like chess or tennis. Children learned to speak by being taught, just as they learned games or sports. This behavioral approach seemed obvious until Noam Chomsky pointed out that this is not how children learn to speak at all. Placed among speakers, they automatically begin speaking, just as plants, placed in moist soil, automatically begin growing. Placed among chess players, however, children do not automatically begin playing chess. It looks as though language ability is innate, like visual ability - an organ rather than a skill.

Just how this peculiar organ evolved is a question that has only just come into its own. In "The First Word," science writer Christine Kenneally narrates the birth and growth of evolutionary linguistics since around 1990. In that year, the young MIT professor Steven Pinker and a graduate student, Paul Bloom, published a paper arguing for increased study of language evolution. An avalanche of work has ensued. Cognitive psychologists have devised experiments to trace the intricate dependence of concepts and processes like time, number, causality, and memory on language. Physiologists have discovered that some essential mechanisms of human speech production are also found in other species. Brain researchers have mapped various aspects of language to areas of the brain that emerged in different eras, throwing light on the stages of language evolution. Child-development researchers have found that gesture is "the preliminary scaffolding of thought," allowing them to predict the pace of a child's language acquisition from its capacity to gesture as an infant. Even geneticists have contributed, with the first discovery of a specific gene linked to an inherited speech disorder.

Kenneally also introduces us to Betty (a New Caledonian crow), Kanzi (a bonobo), and several other critters who are learning communication skills, including language, from their humans. In some cases this teaching is explicit; in others the animals simply learn by being in a language-rich environment, as human children do. Kenneally's reporting and interpretation of this research, whose implications for the study of language and human nature are immense, occupy center stage in "The First Word" and generate real excitement on the page.

Pinker, who kicked off this wave of research, has also just written an ambitious new book about language and human nature. That may sound like a coincidence, but in fact Pinker has always just written an ambitious new book about language and/or human nature. "The Stuff of Thought" manages the unusual (unique?) feat of being the concluding volume of two different trilogies. We might call them the Language Trilogy ("The Language Instinct," "Words and Rules," and "The Stuff of Thought") and the Human Nature Trilogy ("How the Mind Works," "The Blank Slate," and "The Stuff of Thought").

"There is a theory of space and time embedded in the way we use words," Pinker begins. Likewise "a theory of matter and a theory of causality . . . a model of sex . . . conceptions of intimacy and power and fairness," as well as of "divinity, degradation, and danger"; also "a conception of well-being and a philosophy of free will." Teasing out these notions from everyday usage and deconstructing them to show how they function is the task Pinker has set himself. This is conceptual semantics, the theory that "word meanings are represented in the mind as assemblies of basic concepts in a language of thought."

Pinker is a verb maven. The book is filled with lists of verbs, classified, compared, and contrasted by means of subtle logical and conceptual distinctions and grammatical categories. Why do children make some grammatical mistakes often but other, equally plausible ones never? Why do we say "Jane touched John on the arm" but not "Jane touched the building on the window"? These and a hundred similar questions turn out to yield deep insights into our mental structures and processes. And it's all much more enjoyable than you might (unless you're also a verb maven) expect. Pinker is not only wonderfully clear; he is also blessedly witty. There's plenty of stuff to think about in "The Stuff of Thought," but a lot of fun stuff too.

George Scialabba is a regular contributor to the Books section.

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