On Masticatory Muscle and Encephalization Have a look at this article from today's New York Times. It describes how new research has discovered that a particular genetic mutation may have triggered the evolutionary changes that transformed our ape-like ancestors into Homo sapiens. Here's and excerpt:
At a pivotal time in human evolution, around 2.4 million years ago, a muscle gene underwent a disabling alteration, new research has found. And scientists say this may have made all the difference, leading to the enlarged brains of the lineage that evolved into modern humans.
Researchers who made the discovery said this might be the first recognized functional genetic difference between humans and the apes that can be correlated with anatomical changes in the fossil record. The gene mutation, they said, may amount to the beginning of the ancestral triumph of brain over brawn. At the least, they and other scientists said, the mutated gene probably accounts for the more graceful human jaw, in contrast to apes' protruding jaw and facial ridges.
The discovery was made by scientists at the University of Pennsylvania School of Medicine and is being reported today in the journal Nature. The researchers also described the findings in interviews last week.
``We're not suggesting that that mutation alone buys you Homo sapiens,'' said Dr. Hansell H. Stedman, leader of the research team. But, he added, ``it lifted a constraint" that had inhibited brain growth.''