The evolution of verbal behavior.

Evolutionary theory has always been plagued by scantiness of evidence. We see the products of evolution but not much of the process. Most of the story happened long ago, and little remains of the early stages. Especially few traces of behavior remain; only recently were there artifacts that could endure. Verbal behavior left no artifacts until the appearance of writing, and that was a very late stage. We shall probably never know precisely what happened, but we ought to be able to say what might have happened-that is, what kinds of variations and what kinds of contingencies of selection could have brought verbal behavior into existence. Speculation about natural selection is supported by current research on genetics; the evolution of a social environment or culture is supported by the experimental analysis of behavior. Strictly speaking, verbal behavior does not evolve. It is the product of a verbal environment or what linguists call a language, and it is the verbal environment that evolves. Since a verbal environment is composed of listeners, it is understandable that linguists emphasize the listener. (A question often asked, for example, is, "How is it possible for a person to understand a potentially infinite number of sentences?" In contrast, a behavioral analysis asks, "How is it possible for a person to say a potentially infinite number of sentences?") This paper, then, is about the evolution of a verbal environment as the source of the behavior of the speaker. The plausibility of a reconstruction depends in part upon the size of the variations that are assumed to have occurred; the smaller the variations, the more plausible the explanation. Web-making in the spider, for example, could scarcely have appeared all at once in its present form as a variation. More plausible is a series of small steps. The excretion that eventually became silk may have begun