Friday, March 26, 2004

Rosetta stone of human evolution uncovered?

The New York Times (reg'n req'd) has an article by John Noble Wilford about how a mutation has been discovered that decreased jaw muscles in humans.

Selected quote
The researchers' new discovery involves a gene called MYH16, which had apparently gone unrecognized because of a small mutation that had rendered it inactive for producing some jaw muscles for chewing and biting. The scientists found that this myosin gene was still intact today in other primates, like chimpanzees and macaques, which have correspondingly strong jaw muscles. An analysis of DNA samples showed the gene-inactivating mutation to be present in all modern humans worldwide. The analysis further traced the mutation's occurrence to a range of 2.1 million to 2.7 million years ago, probably 2.4 million.

That happens to be just before the appearance of major evolutionary changes in hominid fossils, the research team noted in the journal article. Some hominids with protruding jaws and small brains were soon to evolve into the first species of the genus Homo, with significantly smaller jaws, larger brains and a modern human body size. After a point some two million years ago, Homo erectus was able to strike out for lands far beyond Africa.

"The mutation very possibly initiated an evolutionary cascade," said Dr. Nancy Minugh-Purvis, a Penn paleoanthropologist involved in the project.

Dr. Stedman's group said the findings "raise the intriguing possibility that the decrement in masticatory muscle size removed an evolutionary constraint on encephalization." In short, it may have been the decline of the strong, stoutly buttressed jaw muscles that allowed the skull to develop a new shape and structure, giving the brain room to grow.

I like the phrase evolutionary cascade.

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