Too random to have much effect, I should think. And at the same time, not awful enough to reduce the population to the point where drift would become important. Unless we're talking asteroid impacts.

One can imagine exceptions. For example, if alleles that gave resistance to some deadly plague had negative side effects on intelligence, then you'd see an effect. Note that negative side effects are much more likely than positive side effects.

I know of some neat anecdotal exceptions. Von Neumann got out of Germany in 1930, while the getting was good. When a friend said that Germany was oh-so-cultured and that there was nothing to worry about, Von Neumann didn't believe it. He started quoting the Melian dialogue - pointed out that the Athenians had been pretty cultured. High intelligence helped save his life.