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.
Paabo seems to think it unlikely that any of these introgressed alleles had a a significant selective advantage in humans, but that's unlikely. I'll bet money on this.
To be fair, I should explain why that is a sucker bet. John Hawks and I discussed about a situation with just a few tens of matings over all time: we were making the point that even in that minimal scenario, alleles with large advantages (on the order of 5%) could jump over to modern humans. The Max Planck estimate of 2% Neanderthal admixture is far more favorable to introgression: with that...
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.
I would say that it is some sense obvious that higher intelligence is possible, because the process that led to whatever intelligence we have was haphazard (path-dependent, stochastic, and all that) and because what optimization did occur was under severe constraints - some of which no longer apply. Clearly, the best possible performance under severe constraints is inferior to the best possible with fewer constraints.
So, if C-sections allow baby heads to get bigger, or if calories are freely available today, changes in brain development that take ad...
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 wa...
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 ha...
Better hunting techniques can significantly raise Malthusian limits.
First, you have to remember that old-fashioned humans were one predator among many: improved hunting techniques could raise our share of the pot, as well as decreasing other predators' tendency to eat us. Also, modern humans seem to have used carcasses more efficiently than Neanderthals: they had permafrost storage pits and drying racks, so could have preserved meat for long periods. Neanderthals didn't, and I think they must have wasted a lot. Next, moderns used snares, ...
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.