gcochran

Obviously you can limit travel in any way you want: you can let health workers go in and out while blocking regular travelers. Or, for that matter, you could block everyone under 20, everyone over 40, and everyone called Murphy. It does not have to be all or nothing.

If you were trying to make sense, you would let health workers fly in and quarantine them for three weeks on the way back: that's not much of an inconvenience, considering the risk. And you wouldn't let locals fly elsewhere for the duration.

" Liberia" was short hand: I mean the several countries in West Africa where the epidemic exists.

You know, discussions in this forum have a truly unusual flavor.

Purges in Cambodia might have changed average genotypes because they hit such a high fraction of the population. Generally it's hard to change things much in one generation, though - particularly because of loose correlations between genotypes and dreadful political fates. In the future dictators should be better at this. Now if Stalin had taken all the smartest people in the Soviet Union and forcibly paired them up, artificially inflating assortative mating for intelligence, you would have seen an effect. If you were a billionaire, you could maybe bribe people into something similar.

 There are sub-patterns.   There are facts about natural selection that every plant geneticist knows that few human geneticists will accept without a fight.  I mean, really, Henry, when a prominent human geneticist says " You don't really believe that bit about lactase persistence being selected, do you?" , or when someone even more famous asks "So why would there be more mutations in a bigger population?"  -  their minds ain't right. 

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.

Hawks and I were talking about new genetic studies that showed a surprising number of sweeps, more than you'd expect from the long-term rate of change - and simultaneously noticed that there sure are a lot more people then there used to be - all potential mutants.

As for why someone didn't point this out earlier - say in 1930, when key results were available - I blame bad traditions in biology. Biologists mostly don't believe in theory: even when its predictions come true, they're not impressed.

My advantage, at least in part, comes from have had exactly one biology course in my entire life, which I took in the summer of my freshman year of high school, in a successful effort to avoid dissecting. If I ever write a scientific autobiography, it will be titled "Avoiding the Frog".