Interesting line of defence Cofty. I thought you'd more straightforwardly point out that evolution doesn't necessitate humans getting smarter. Being dumber or having a smaller brain could equally have selective advantages. In fact I think some have argued humans are getting dumber. The opposite of the Flynn effect.
Intriguing statement Slimboyfat. After having read Evolution is a fact #9 - Less Chewing More Thinking, do you believe that "the MYH16 gene in humans that produces a protein called myosin heavy chain 16" will react on smaller brain size and return to bigger temporalis muscles? You know, like primates such as the chimpanzee or even the gorilla where this protein produces their powerful chewing pressure of the jaw.