Copyright © 1998 by McGraw-Hill, Inc. All rights reserved. Printed in the United States of America. The entire contents or parts of this Update may be reproduced for use with Physical Anthropology, Sixth Edition, or Physical Anthropology: The Core, second edition, by Philip L. Stein and Bruce M. Rowe, provided each reproduction bears the copyright notice. The publisher's written permission must be obtained for other use.
See Physical Anthropology, 6th edition, Chapter 12, pages 291-295; Physical Anthropology: The Core, 2nd edition, Chapter 8, pages 208-209.
Attempts at teaching chimpanzees how to speak began almost a century ago. By about 50 years ago, most scientists concluded that chimpanzees did not have the neurological potential that would allow them to speak. For one thing they seem to lack an area of the brain called Broca's area that in humans controls the muscles of the vocal apparatus in the production of speech. Also, the different hemispheres (left and right) of the human brain are specialized for different functions. This lateralization seemed absent in most other animals.
In most humans, many of the areas associated with language, including Broca's area, are housed in the left hemisphere. Another area, Wernicke's area, is also usually located in the left side of the brain. This area deals with the comprehension of language.
The terms language and speech are not synonymous. Language is a system of communication that uses abstract symbols to represent meanings. Speech is a way of delivering linguistic information by using sounds to represent meaning. Writing is also language and uses graphic symbols to represent meaning. Sign language uses hand signs to convey meaning.
When it was discovered that it was not apparently possible to teach chimpanzees speech, researchers shifted to sign language. Numerous chimpanzees, as well as some gorillas and orangutans, have been taught sign language. However, critics of these studies state that the chimpanzees were most likely learning to use the hand signs through conditioning, mimicking, subtle cues from a researcher. The critics also pointed out that the chimpanzee brain did not have the areas of the brain equivalent to those humans possess for processing language-that is, Wernicke's area.
Now there is new research that indicates that chimpanzee brains may be lateralizated in a manner similar to that of humans in the area that includes Wernicke's area. The research, done by Patrick J. Gannon, Ralph L. Hollowasy, Douglas C. Broadfield, and Allen R. Braun, concludes that as with humans, a section of the brain called the planum temporale is larger in the left hemisphere of the chimpanzee then it is in the right hemisphere.
In humans, Wernickes' area makes up the entire planum temporale. Whether the larger size of the planum temporale in the chimpanzee relates to a potential for language comprehension, or functions in some other way, remains to be seen.
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References: P.J. Gannon et al., "Asymmetry of Chimpanzee Planum Temporale: Humanlike Pattern of Wernicke's Brain Language Area Homolog," Science, 279 (January 9, 1998), 220-222; B. Bower, "Chimpanzee Brains Show Humanlike Tilt to Left," Science News, 153 (January 10, 1998), 22.