Culture – memetic variation and selection – is the medium of Lamarckian evolution. Culture is the way that humans pass along acquired characteristics – learned ideas – to their fellows and heirs. And ideas have consequences. Our ideas shape how we live, and thus where, when, and how long we live, how many children we have and how we raise them, or not, how we coordinate our activities, and so forth. The structure of social coordination evolves.
As factors of prosperity and reproductive success, ideas have genetic consequences. And those genetic consequences feed back into the selection of cultural memes.
So there is coevolution of genes and culture. Men prosper in cultures to which they are physiologically well fitted, and cultures prosper among men who are physiologically equipped to enact their memes. Their physiological equipment includes the structure and organization of their nervous systems.
Men and women of a given thede, then, are likely to be better adapted physiologically to the cultural forms historically predominant in that thede. This is why Swedes do better than the Ik at Social Democracy.