Given that various mental disorders are heritable, it's not clearly impossible for psychological properties to be selected for.
However, unlike dark or light skin (which matters for dealing with sunlight or the lack of it), mental ability is generally useful for survival and success in all climates and regions of the world. Every physical and social setting has problems to figure out; friendships and relationships to negotiate; language to acquire; mates to charm; rivals to overcome or pacify; resources that can be acquired through negotiation, deception, or wit; and so on. This means that all human populations will be subject to some selection pressure for mental ability; whereas with skin color there are pressures in opposite directions in different climates.
So why is this such a troublesome subject?
The problem with the subject is that there's an ugly history behind it — of people trying to explain away historical conditions (like "who conquered whom" or "who is richer than whom") in terms of psychological variation. And this, in turn, has been used as a way of justifying treating people badly ... historically, sometimes very badly indeed.
Classifications don't exist for themselves; they exist in order for people to do things with them. People don't go around classifying things (or people) and then not doing anything with the classification. But sometimes people make particular classifications in order to do horrible things, or to convince other people to do horrible things.
"Earthmen are not proud of their ancestors, and never invite them round to dinner." —Douglas Adams
There is a tradeoff between energy consumption and intelligence (where the optimum has moved toward a focus on intelligence with our species). Your second paragraph doesn't eliminate the possibility that this optimum might have landed at different points in different ancient locations.
The most recent post in December's Stupid Questions article is from the 11th.
I suppose as the article's been pushed further down the list of new articles, it's had less exposure, so here's another one for the rest of December.
Plus I have a few questions, so I'll get it kicked off.
It was said in the last one, and it's good advice, I think:
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.