Weaker jaw, stronger thought

From Less Jaw, Big Brain: Evolution Milestone Laid to Gene Flaw by John Noble Wilford.

''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.