(Philadelphia, PA) In an effort to find the remaining genes that govern myosin--the major contractile protein that makes up muscle tissue--researchers at the University of Pennsylvania School of Medicine have made a discovery that may be central to answering key questions about human evolution.

Published in the March 25 issue of Nature, Penn researchers have found one small mutation that undermines an entire myosin gene. Their estimated dating for the appearance of this mutation places it at about 2.5 million years ago, just prior to a period of major evolutionary changes in the hominid fossil record. These include the beginning of larger brain size, so important in making us human. While the characterization of this mutation may better help understand such genetic diseases as muscular dystrophy, this finding has potentially wider implications for re-interpreting long-held notions about the appearance and early evolution of the genus Homo.

Anthropologists have long debated how humans evolved from ancestors with larger jaw muscles and smaller brains. This newly discovered mutation seems responsible for the development of smaller jaw muscles in humans as compared to non-human primates. These converging lines of evidence suggest the question: Did this genetic mutation lift an evolutionary constraint on brain growth in early humans?

In a classic case of scientific sleuthing, Hansell Stedman, M.D., Associate Professor of Surgery, Nancy Minugh-Purvis, Ph.D., Director of Advanced Gross Anatomy, Department of Cell and Developmental Biology, and colleagues took their discovery of a mutation that prevents the expression of a variety of myosin -- designated MYH16 on chromosome 7 -- to its ultimate context: what makes humans different from other primates.

"Around the lab, we jokingly call this the 'room for thought' mutation, since we had to involve scientists from several disciplines to make sense of the possible domino effects," says Stedman. "In
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Contact: Karen Kreeger
karen.kreeger@uphs.upenn.edu
215-349-5658
University of Pennsylvania School of Medicine
24-Mar-2004

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