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The launch of language |
| TheAllINeed.com |
(NC&T/UCB) Berkeley professor of anthropology Terrence Deacon takes a very different view. His research into neurobiology and brain development indicates that our species attained its silver tongue in a far less dramatic manner. The human flair for language, he says, emerged in the very same way as all other body structures: in the embryological minuet between evolution and development.
"In development, brains adapt to the body they find themselves in," Deacon says. For example, if an extra limb or eye is are grafted onto a frog during development, the embryo grows nerves to make the new appendage functional, despite the fact that its DNA contains no instructions for coping with extra organs. "It's an embryological adaptation process, in which the wiring becomes fitted to both the populations of neurons and muscles and the kinds of signals that have to be carried around."
Our language facility, Deacon writes in his award-winning 1997 book The Symbolic Species, was an adaptation to a new set of environmental needs. About two and a half million years ago, our ancestors made a radical shift in culture: they began using stone tools to scavenge meat on the open savanna. They had to cooperate in small social groups to compete with other animals for downed prey. At the same time, such social closeness sparked conflicts over food resources and mates. To overcome these challenges, early hominids needed an unprecedented form of communication.
The human knack for speech requires a high degree of neural complexity. Conducting even the simplest conversation requires input from multiple areas of the brain. Most biologists consider greater complexity the result of intensified natural selection. Deacon, however, thinks that the neural architecture for language was the brain's response to a release from natural selection. In recent research and his upcoming book, Homunculus, Deacon shows that devolution can bring developmental plasticity to the fore.
He cites the evolution of song in the Bengalese finch. In 300 years of domestication, the bird's song has changed radically from that of its ancestor, the white-rumped munia. Where the munia is a chirping automaton, using one brain structure to make a simple, unlearned, unvarying song, the Bengalese finch is a font of musical creativity. It shuffles song phrases, copies tunes from other birds, and uses multiple brain structures to learn, acquire, and control its melodies.
Yet all selection on the finch's song was eliminated by its human owners, who bred the birds solely for their plumage.
 | | Parallels between song proccesing in birds and language proccesing in humans (Photo: Terrence Deacon) |
"Ironically, shielding them from any sexual selection affecting song produced a brain radically more complicated for the control of song," Deacon says. "With the degradation of tight song control, cross-talk between connected brain structures that previously didn't play any role now allowed auditory memory, motor learning, and social biases to influence the structure and production of song."
Like the munia, chimpanzees use instinctive, stereotypic vocalizations closely tied to aggression, fear, or other emotions. In humans, the emergence of tools and cultural processes relaxed those rigid vocalization patterns, setting the stage for an explosion of linguistic invention. Unlike other animals, "human babies start babbling in a relaxed, nonemotional state early in life," Deacon says. "A significant part of our ability to do language is the result of loosening up those constraints."
The evolution of language, Deacon says, "was not just nature versus nurture. Our language adaptation reflects the special demands of symbols, in much the same way as beaver bodies reflect the demands of the ponds they create. We're a biological expression of culture."
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