[Junior]

First of all, having a larger brain doesn't do you a squat of good unless you are equipped to use it.

The extra brain matter didn't show up all at once. The species had generations to evolve intelligence, with each generation being a skosh more clever than the last, but not orders of magnitude so.

[explodingspleen]

The extra brain matter didn't show up all at once. The species had generations to evolve intelligence, with each generation being a skosh more clever than the last, but not orders of magnitude so.

I quoth myself:
"the increase in intelligence cannot be slight because the advantage it confers on the creature must surpass the detriment it suffers from the weakened jaw which would impair its capacity for self defence and possibly restrict its diet. So there is no gradual evolution--it has to happen all at once."