Once language started, whether in the form of word or gesture or both, its further evolution would doubtless have been rapid because of the great advantages that each improvement in this powerful faculty would have conferred on its possessors. Even while still in its most rudimentary form, language would have made possible a whole new level of social interactions. Precise and unambiguous thoughts could at last be shared among members of a community, whether for making alliances, indicating intention, describing people and places, or transmitting knowledge. Moreover each small improvement in the overall system, whether in precision of hearing or articulation or syntax formation, would confer further benefit, and the genes underlying the change would sweep through the population.
But easy as it is to see how a simple form of language might have evolved into a complex one, that doesn't answer the question of what particular stimulus brought language into being in the first place.
Language now plays so many roles in human society that it's hard to arrange them in some hierarchy and say one role was the root and the others its branches. But evolutionary psychologists have come up with several interesting suggestions about the possible pressures for language to evolve. Robin Dunbar at the University of Liverpool in England has proposed a "social grooming" theory of language. He notes that monkeys and apes spend an inordinate amount of time grooming each other's fur. This activity, besides curbing parasites, serves to cement social relationships. But social grooming sets a limit on the size of a monkey group, because members will have no time to search for food if there are too many acquaintances whose fur must be rubbed the right way.
In practice, different monkey species spend varying amounts of time on grooming one another, up to a maximum of 20% of their waking day, and this is among species whose typical group size is about 50 members. The maximum time available for social grooming, Dunbar argues, has effectively capped the size of monkey social groups at 50 members. How then did the typical size of hunter-gatherer groups grow to 150 members, a number that would in principle require everyone to spend 43% of their waking hours on social grooming, or its human equivalent? Because of language, Dunbar suggests. Language is so much more efficient a way of establishing and confirming social bonds that the requisite amount of social grooming could be cut way back. In a wide range of human societies, it so happens, the amount of time people spend in social interaction, or conversation, is 20%. The driving force behind the evolution of language, in Dunbar's view, was the need to bond people in larger social groups.^
A quite different explanation has been advanced by the evolutionary psychologist Geoffrey Miller. He believes that sexual selection—Darwin's theory that the peacock's tail is the evolutionary product of peahens' choices—is what has driven the evolution of language. Just as the richness and symmetry of the peacock's tail signals its freedom from parasites, so eloquence and articulate speech signal the quality of an individual's mind, and will be highly favored by both men and women in their sexual partners. Language is a device that lets us learn about potential mates more thoroughly than any other 52
method, Miller writes.
The Dunbar and Miller hypotheses are both evocative and each may hold some measure of truth. But it's not clear if either really accounts for the richness and precision of language. Most adult speakers of English have a vocabulary of 60,000 words, though the top 4,000 words account for 98% of conversation. Does one really need 60,000 words, or even 4,000, for the purposes of social grooming, or even impressing one's inamorata? Miller's answer is that excess is the hallmark of sexual selection—once selection has started, the character under selection is taken to extremes, like the stag's enormous antlers. But for linguists, the essence of language is meaning and communication, and it seems unsatisfactory to explain its evolution on any other grounds. Pinker argues one should take into account the new ecological niche that humans had moved into, which was in fact a knowledge-laden environment requiring a wealth of new information about plants and animals, about how to make tools and weapons, and about goings-on in one's own society. People's longer life span made it worthwhile to gather information and transmit it to one's children and grandchildren. "Language," Pinker says, "meshes neatly with the other features of the cognitive niche. The zoologi cally unusual features of Homo sapiens can be explained parsimoniously by the idea that humans have evolved an ability to encode information about the causal structure of the world and to share it among themselves. Our hy persociality comes about because information is a particularly good commodity of exchange that makes it worth people's while to hang out together."
Pinker concludes that know-how, sociality and language are three key features of the distinctively human lifestyle and that the three factors coevolved, each acting as a selective pressure
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