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ON LANGUAGE AND HUMAN INTELLIGENCE

The following points are made by David Premack (Science 2004 303:318):

1) Humans have acquired six symbol systems: two that evolved -- the genetic code and spoken language -- and four that we invented: written language, arabic numerals, music notation, and labanotation (a system for coding choreography). Dobzhansky's quip "All species are unique, but humans are uniquest" raises the question: Is it language, the symbol system that evolved only in humans, that makes humans the "uniquest"? Dobzhansky's quip also raises a more fundamental question: What exactly is the nature of human uniqueness?

2) The grammar or syntax of human language is certainly unique. Like an onion or Russian doll, it is recursive: One instance of an item is embedded in another instance of the same item. Recursion makes it possible for the words in a sentence to be widely separated and yet dependent on one another. "If-then" is a classic example. In the sentence "If Jack does not turn up the thermostat in his house this winter, then Madge and I are not coming over," "if" and "then" are dependent on each other even though they are separated by a variable number of words (1-3). Are animals capable of such recursion? Fitch and Hauser (4) have reported that tamarin monkeys are not capable of recursion. Although the monkeys learned a nonrecursive grammar, they failed to learn a grammar that is recursive. Humans readily learn both.

3) The lack of recursion in tamarins may help to explain why animals did not evolve recursive language, but it leaves open the question of why they did not evolve nonrecursive language. Recursion is not, of course, the only preexisting faculty on which the evolution of language depends.

4) A laboratory chimpanzee does not call to attract the attention of its trainer; instead, it pounds on a resonant surface. Similarly, when chimpanzees become separated in the compound, they do not call to one another, as humans would, but search silently until they see one another and then rush together. If, as the evidence suggests, vocalization in the chimpanzee is largely non-voluntary (reflexive), speech could not have evolved. But then why don't chimpanzees sign to each other? The chimpanzee has voluntary control of its hands. However, sign language depends on the face as well as the hands, and facial expression in the chimpanzee is evidently as reflexive as vocalization. Facial expressions play linguistic roles in signing, such as denoting the boundaries of clauses. A signer processes emotional facial expression in the right hemisphere, but linguistic facial expression in the left hemisphere (5). This does not mean, of course, that chimpanzees could not have evolved a language based on pounding on resonant surfaces, arranging stones on the ground, and so on. But it does suggest that they could not have evolved one that is like either speech or sign. (Of course, speech and sign "travel" with the speaker in a way that stones and resonant surfaces do not.)

5) What are the factors that distinguish human intelligence? A major distinctive feature of human intelligence is flexibility. Animals, by contrast, are specialists. Bees are adept at sending messages through their dances, beavers at building dams, the nuthatch at remembering the location of thousands of caches of acorns it has buried. But each of these species is imprisoned by its adaptation; none can duplicate the achievement of the other. The nuthatch cannot build dams; bees do not have an uncanny memory for hidden caches of food; beavers cannot send messages. Humans, by contrast, could duplicate all these achievements and endlessly more. Why? Is recursive language the key to human flexibility?

6) Human intelligence and evolution are the only flexible processes on Earth capable of producing endless solutions to the problems confronted by living creatures. Did evolution, in producing human intelligence, outstrip itself? Apparently so, for although evolution can do "engineering", changing actual structures and producing new devices, it cannot do science, changing imaginary structures and producing new theories or explanations of the world. Clearly, language and recursion are not the sole contributors to human uniqueness.

References (abridged):

1. N. Chomsky, Syntactic Structures (Mouton, The Hague, 1957)
2. S. Pinker, The Language Instinct (Morrow, New York, 1994)
3. M. D. Hauser, N. Chomsky, W. T. Fitch, Science 298, 1569 (2002)
4. W. T. Fitch, M. D. Hauser, Science 303, 377 (2004)
5. E. L. Newport, T. Supulla, in The MIT Encyclopedia of the Cognitive Sciences, R. Wilson, F. Keil, Eds. (MIT Press, Cambridge, MA, 1999), pp. 758-760

From: ScienceWeek http://scienceweek.com