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.
Those who are anywise poorly fitted to the terms of a culture – who are odd, or weird, or defective – do poorly. They are poorer than average, so that they die earlier, and with fewer issue; or else are killed outright, or banished. Foreigners likewise have a harder time anywhere than natives do.
In seeking to do well, it is only natural that foreigners should seek both to shape themselves to their strange cultural environment, and – as humans always do – shape that environment to themselves. Foreigners introduce memetic dissonance to the transactions of a thede.
Introduce enough foreign memes into a culture, and memetic noise begins to mask its signals. More and more of its quotidian transactions are hampered by the need to translate signals from one language and cultural memeplex into another, and to practice due diligence with all counterparties. Trust – confidence among interlocutors engendered by their perception that diligence is satisfied – is less and less pervasive. The friction, cost, and physiological stress of the business of life then compound. As they more and more devour the marginal value of social transactions, society is more and more impoverished: there is less value to be gained by transactions, so there are fewer of them, and they are both smaller and shallower. At the margin, capital formation of all sorts suffers, and with it the social capacity to respond to challenges or exploit opportunities via capital investment in the provision for its future activities: in plant, equipment, real estate, education, research, exploration, and development. The poorer society gets, the poorer will it get.
As foreign influences increase upon it, a culture will sooner or later begin to decohere. Its memeplex will no longer predominate in the body politic. And then the memetic population that had once evolved symbiotically with its original genetic host will become more and more antagonistic to its progenitor. The genes that evolved to support the culture that has now been deranged by invading memes will begin to suffer something like the graft versus host disease that always threatens bone marrow recipients.
It is then for such a culture as it is for an organism beset by a parasite or virus: performance degrades, there is disease – lassitude, inflammation, fever, nausea, diarrhea, purgation. Or, if these procedures are ineffective at eliminating the invader, death.
It’s all very simple.