Food for thought in evolutionary clue
By Rick Weiss
The evolutionary split between early humans and apes may have begun with a tiny mutation in a gene for jaw muscles -- a lucky break that allowed the skull to grow and make room for the enormous brain that would eventually become the hallmark of Homo sapiens.
That's the controversial conclusion of researchers from the University of Pennsylvania, whose discovery of the mutation, announced Wednesday, has fanned the long-smoldering debate over how, exactly, modern humans evolved.
The Penn team's work suggests that early primate skulls -- much like the skulls of modern gorillas and chimpanzees -- were literally muscle-bound by powerful jaw muscles and cramped by the big bony spurs that anchored them. Only when a quirk of nature produced mutants with radically smaller jaw muscles was the skull free at last to expand over the generations.
The rest, as the team said, is human history.
``The going joke around the lab is that this is the `rft' mutation -- the `room for thought' mutation,'' said Hansell Stedman, who led the new work, being published in today's issue of the journal Nature.
``I love this paper. It's perfect,'' said University of Michigan paleoanthropologist Milford Wolpoff.
However, ``Let's see,'' quipped the more skeptical Tim White of the University of California-Berkeley, by e-mail. ``We got big brains because little muscles . . . didn't hold the cranial bones tightly together. I may stop chewing tonight.''
But supporters and critics of the Penn proposal agreed that it was an important scientific first to have found a genetic mutation that apparently occurred just when significant physical changes were occurring in pre-humans, as documented by a number of fossil finds.
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