Gene Mutation of Jaw Linked to Brain Evolution; Deactivated Muscle Facilitated Tripling of Size, Researchers Say

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Byline: Joyce Howard Price, THE WASHINGTON TIMES

Human evolution may have hinged on a genetic mutation 2.4 million years ago that weakened the jaws of prehistoric man and allowed the development of bigger brains, say U.S. researchers.

This hypothesis was reported in this week's issue of the scientific journal Nature by a team of biologists, anthropologists and plastic surgeons at the University of Pennsylvania Medical School and Children's Hospital of Philadelphia.

Dr. Hansell Stedman, the study's lead author, said he and his colleagues are "not suggesting that this mutation alone defines us as Homo sapiens."

But he added: "Evolutionary events are extraordinarily rare. Over 2 million years since the mutation, the brain has nearly tripled in size. It's a very intriguing possibility."

Richard Potts, director of the Human Origins Program at the Smithsonian Institution, said the scientists clearly pinpointed a genetic mutation in early man that deactivated the big jaw muscles found in nonhuman primates that allow them to bite and grind tough food.

But Mr. Potts called the researchers' premise that this ancient gene mutation may have led to brain growth and human evolution "way too speculative."

In their published study, researchers described how they isolated a new gene on Chromosome 7 as part of a medical search for human genes linked to a family of proteins called myosins that make muscles contract.

They discovered a new myosin gene, called MYH16, that had one small mutation that made it inactive. This mutation was found to be present in all the humans they tested from Europe, Africa, Asia and South America.

But when they analyzed the DNA of seven species of apes, including chimpanzees, all the animals had the active, rather than the mutated, form of the gene. …