Hominid brains: advanced or apelike?
The disagreement centers on two researchers, Ralph L. Holloway of Columbia University in New York and Dean Falk of the University of Puerto Rico in San Juan. In the Jan. 3 NATURE, Falk reports that the bumps and grooves made by the outer, or cortical, layer of the cerebrum on the inside of a 3-million-year-old Australopithecus afarensis skull indicate that the brain was "small, simple and apelike." Australopithecines who came after this earliest known hominid and larger brains but similar cortical patterns, adds Falk. Hominid brains probably got larger before they became more complex, she argues.
In a previous analysis of the same hominid skull, Holloway came to a drastically different conclusion. Although the brain was rather small, there is evidence that its outer layer was undergoing reorganization, he explains. "There appears to have been enlargement of the posterior parietal, or 'association' area," says Holloway. This section of cortex integrates visual stimuli with other stimuli and would have played an important role in the development of social behavior. He further suggests that an increasingly complex brain was associated with the emergence, around 3 million to 4 million years ago, of walking on two feet.
Holloway, along with William Kimbel of the Institute of Human Origins in Berkeley, Calif., claims that Falk "mis-oriented" the cast she took of the hominid brain case. "Falk improperly rotated the cast forward and down by approximately 30 degrees," says Kimbel, who has studied casts of the same skull. When rotated back, the skull tells a different story. They cerebellum, a primitive part of the brain located under the cerebrum, moves under the occipital poles of the cortex into a humanlike position, says Holloway. In Falk's version, the cerebellum juts beyond the occipital poles, suggesting a less developed brain.
"This is a continuation of an ongoing disagreement," says Falk (SN: 7/2/83, p. 11). "I've carefully checked my orientation of the skull and am satisfied with it." Kimbel, she adds, has written that depressions made by the cerebellum on the same skull are deeper than those made by the cortex. Falk says this supports her contention that the cerebellum projects back farther than the occipital poles. Kimbel, however, says his observation does not necessarily buttress her conclusion.
It is a bit baffling that the same skull could produce such varying interpretations, but science marches on. "In a way, Falk has done a valuable service," says Holloway. "We now can test her assertions."
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|Date:||Mar 9, 1985|
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