The Gestural Origins of Language
Human language may have evolved from manual gestures, which survive today as a "behavioral fossil" coupled to speech
Consider first some facts about primate evolution. Primates are largely visual animals, perhaps as a result of a common adaptation to visual predation. In people as in monkeys, vision is much more highly developed than any other sense modality, including hearing. Further, with the exception of humans, primates have much better cortical control over movements of the hands than over vocalization, which is largely restricted to emotionally based sounds controlled by subcortical structures. This means that the early hominids would have been much better preadapted for expressive, voluntary communication using the hands, and it perhaps explains why attempts to teach chimpanzees a version of sign language have been much more successful than attempts to teach them anything resembling human vocal language. In one early study, for instance, a chimpanzee raised in a human family could learn to speak only three or four words, whereas gorillas (such as Koko at the Gorilla Foundation) and chimpanzees (such as Washoe and Tatu, now at the Chimpanzee and Human Communication Institute) have been successfully taught several hundred manual signs to represent different objects or actions.
Reciprocity of gesture, as a precursor to language, may go back even further, to our common origins with apes and monkeys perhaps 25 or 30 million years ago. Giacomo Rizzolatti and his colleagues at the University of Parma in Italy have recorded from single neurons (in the premotor cortex of monkeys) that are active when the monkeys make particular gestures of reaching. Some of these neurons, which Rizzolatti and his colleagues have dubbed mirror neurons, are also active when the monkeys watch a person (or, presumably, another monkey) making the same gesture. These cells are in an area of the monkey cortex that appears to be homologous to Broca's area in the human brain, which is critically involved in the programming of human speech. Mirror neurons presumably have more to do with giving and receiving items of food than with language, but Rizzolatti and Michael A. Arbib, a computer scientist at the University of Southern California, have proposed that they are preadaptations for the subsequent elaboration of language. They may also be precursors of the ability to take the mental perspective of others, which Byrne and others have regarded as necessary prerequisites for language.