Bite makes way for brain

A single mutation may have caused gross anatomical changes that spurred human evolution | By Brendan A Maher

A pile of evidence from disparate disciplines indicates that a single change in a single gene—MYH16—may be responsible for significant morphologic differences between humans and other primates, including possibly the three-fold increase in brain size that set the earliest species of Homo apart from their kin. This is the first protein disparity between humans and chimps that can be correlated to drastic anatomical changes seen in the fossil record, according to a group of University of Pennsylvania researchers who published a letter in the March 25 issue of Nature.

“This is a brilliant piece of detective work that has enormous implications for medicine, biology, evolution, molecular genetics, [and] the human genome,” said Frederick S. Kaplan, a professor of orthopedic molecular medicine at Penn who was not part of the study. “By relegating a gene to the evolutionary garbage heap, we were able to lift the constraints to the development of human complexity,” he told The Scientist.

Powerful muscles for biting practically dominate the cranial structures of most primates, including gorillas, chimps, and extinct Australopithecus and Paranthropus species. A gene responsible for a majority of jaw musculature was lost from human ancestors, presumably 2.4 million years ago, according to the study. Drastic reductions in these muscles may have lifted significant physical constraints on braincase volume, allowing primates with weak jaws and big brains to eventually think about their origins.

It makes no sense to me.

If the human ancestor lost the gene for strong muscle it had still no extra brain to compensate for the obvious loss of fitness.

It would have to compete with same-brained, better jawed specimens.

what do you think?