Genetics seems to play a key role in the development of culture and social structure. If you move 1M Mexicans in Tokyo, their offspring will not act like Japanese people do, regardless of the environment. They would exhibit different behavioral and voting patterns.
Large groups of people carry characteristic sets of genes which drive behavioral patterns, as well as culture which also drives behavioral patterns. On a large scale, the differences between Japanese and Mexicans are driven by cultural and genetic differences.
The degree, balance, and nature of those differences is complex and up for debate, of course. But to state that Japanese and Mexicans have no distinguishing behavior-driving genes at all even in the slightest degree is basically the left-wing version of young-Earth creationism.
As far as I can tell (again, in my relative ignorance), the assertion that "genetics seems to play a key role in the development of culture and social structure" is just as foolish and unsupported as the claim that you dismissed.
Would it not be completey bizarre if there were zero differences in the one most complex organ we do not understand?
Would you argue that no group of people are taller? Or could run faster? Or perhaps have varying levels of visual acuity? What would cause such differences to suddenly just completely stop because it's related to the brain?
Meanwhile, there are lots of different genetic groups making up America, even within a race - the American definition of "white" is extremely genetically diverse and contains lots of backgrounds that have formed separate identities in Europe, and you don't see a lot of cultural separation on those lines. You see cultural separation on visible lines like actual skin color, language, recency of immigration, etc. But all of that is more easily explained by humans making conscious choices to associate with certain people we think are like ourselves, not genetics.
Tendency towards aggression, as your paper shows, is an individual characteristic, and something that can be overridden in either direction by social norms. (Even within a fairly homogenous genetic group, there's a huge amount of individual variation in aggressiveness.) I'm certainly happy to concede that genetics matters a lot at the individual level, but it's a large leap to find that it matters at the cultural level. If you introduce one million people without (or with) this gene slowly into a culture of people with (or without) this gene, letting them assimilate, letting them have children and raise them within the existing culture and intermarry, would we expect a chance in cultural norms for people with this genetic background? Possibly, but I certainly wouldn't expect one.
[x]Various studies have found the heritability of IQ to be between 0.7 and 0.8 in adults and 0.45 in childhood in the United States. It may seem reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. However, that the opposite occurs is well documented. https://en.wikipedia.org/wiki/Heritability_of_IQ#estimates
Yes, and I assumed this was obvious. I did say "expect", after all. But a large-N experiment where each child is in the "isolated" condition is totally different from a large-N experiment where a large population is transplanted.
> Migratory waves are not made of 1 infant with no parents.
Whether immigrant communities preserve culture etc is not in question. I'm only refuting the point that there is a large genetic component, and your argument here effectively concedes that.