A genetic loss approximately 2.4 million years ago may have made cranial room for the bigger brains that characterize our direct evolutionary predecessors. That proposal comes from researchers who have discovered a DNA deletion that occurs in people but not in other primates.
In what started out as a search for genes linked to muscular dystrophy, a team led by surgeon Hansell H. Stedman of the University of Pennsylvania School of Medicine in Philadelphia found that only people possess an inactivated version of a gene involved in facial-muscle movements. As a result, the gene fails to produce a variant of the protein, called myosin, that powers muscles used in biting and chewing, the scientists report in the March 25 Nature.
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