In March, I wrote a post on some tantalizing new findings about the secrets of human evolution lurking in our genome. In brief, researchers at the University of Pennsylvania studied a gene called MYH16 that helps build jaw muscles in primates. In our own lineage, the gene has mutated and is no longer active in jaw muscles. Perhaps not coincidentally, we have much smaller, weaker jaws than other apes. The researchers estimated that the gene shut down around 2.4 million years ago–right around the time when hominid brains began to expand. They suggested that shrinking jaw muscles opened up room in the hominid head for a larger brain.

It’s a cool hypothesis, but it may not hold up. Scientists at Arizona