To answer your question, a lot of paleontologists believe that hominid dietary changes from cooking, which came before Homo sapiens and somewhat after the genetic change mentioned in the submitted article, eliminated selection pressure in favor of strong chewing power, because food became softer, more digestible, and thus more nourishing. This allowed the ancestral line to Homo sapiens to devote more total bodily energy to growing a large brain (also enabled by the mechanisms mentioned in the submitted article) and much less energy to developing a hindgut that can digest raw vegetable foods. So there were several synergistic influences that allowed a diverging body plan between the chimpanzee line and the Homo sapiens line.

This Economist article (previously submitted to HN)

http://www.economist.com/science/displaystory.cfm?story_id=1...

tells part of the story. HN discussion here:

http://news.ycombinator.com/item?id=490292