[AntiGuv]

One may also posit that since increased intelligence is such an obvious evolutionary advantage, that the primates with weaker jaws would swiftly begin evolving larger brains in relatively few generations time. Those weak-jawed primates born with larger brains would have a higher probability of surviving to reproduction than those weak-jawed primates with smaller brains (independent of the jaw-strength) and so once the genetic provision was made that allowed for larger brains, they would quickly expand to fill the available space and thus become the norm.

[js1138]

One may also posit that since increased intelligence is such an obvious evolutionary advantage...

There are folks who belive that big brains in mammals are a result of sexual selection, which is to say that smarter guys get more chicks. Consider your brain to be equivalent to a rack of antlers. Or in the case of democrats, a flaming red butt.