Racial differences...

[Moros]

What mutations you get is random, that's what I am getting at. Even if the the enviroment in itself does not require better cognitive capabilities, that doesn't mean that such traits are more favourable and will give rise to better chances of survival.

But if they don't give better chances of survival they usually don't spread over the population and eventually dissapears from it's genepool. Unless the population is really small.

Edit: unless it improves chances of mating. For example a comparison between gorilla balls (really small as there's only one male ape who get's down with the ladies) and chimps (who all try to get it down and hence have been competing for generations for having the best balls).