Brain Size Surprise: All primates may share expanded frontal cortex

9:55am, March 10, 2004

Researchers have traditionally theorized that the frontal cortex, a brain region linked to mental faculties such as planning and reasoning, expanded to an unprecedented extent during human evolution. However, a new analysis of brains from many different mammals takes the uniqueness out of our frontal cortex.

Lemurs, gibbons, chimpanzees, and other primates have roughly the same proportion of brain tissue devoted to the frontal cortex as people do, say Eliot C. Bush and John M. Allman of the California Institute of Technology in Pasadena. Lions, hyenas, and other carnivores display a substantially smaller frontal cortex relative to the rest of the brain.

"People aren't special in regard to frontal-brain size," Bush says, "but there appear to be important differences between primates and carnivores in the way the frontal cortex is put together."

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