Plomin is and always has been careful not to talk about questions outside his immediate research, because they’d get him in trouble. He reaps more than enough trouble just doing his job. So much so that he sometimes says ridiculous things just to avoid trouble, like saying that nobody knows what causes male-female differences. It is to laugh. Yeah, we know that one.
What about inter-population differences in personality and intelligence? Are they driven by mystic factors insusceptible to the scientific method, as Mr. T suggests? Of course not. Since they exist in populations going to the same schools, eating approximately the same food, watching similar TV – since they show up by age three – you can rule out a lot of causative factors. Generally, anything that would fall into the shared-environment category doesn’t seem to explain it, just as it doesn’t explain within-pop differences. In most developed countries anyhow: in some places factors like iodine deficiency play a role.
We could talk about structural racism, but since it does not exist, why bother? I’d rather talk about the aether.
Probably the causes of between-population differences are the same kind of genetic factors that explain most variation between individuals in a population – systematic differences in the frequencies of many alleles of small effect. Probably this explains the differences between populations that lived in different eras as well: with better recovery of ancient DNA, we might be able to detect historical trends.
Could genetic differences have an effect on the flavor of culture in different populations? Well, even allowing for differences in intelligence: sure. Identical twins like the same things, pick similar clothes, read similar authors: genetically different populations could and must have different tastes and preferences, on average.