In-marriage Out-marriage oscillation

Previously (Group Selection of Humans) I convinced myself that humanity finds a balance between in-breeding and out-breeding. I now think that the balance is more like an oscillation, as balances often are. Here’s the story:

There was a discussion about ISIS that seemed to assume that male talk was the full story (https://plus.google.com/u/0/117663015413546257905/posts/5DfjTXF5agm). I tried to suggest more real-world reasons for the vigorous opposition to Western values:

An interesting aspect of the IS area is that a lot of marriages are to cousins, preserving family power and status. The great threat to family status is female education and power from merit. I suspect that it would be useful to understand female opinion in the area as well as listening to the cacophony of males talking about arcane knowledge.

Which everyone ignored, except for David Friedman who responded:

"An interesting aspect of the IS area is that a lot of marriages are to cousins"

Any more than elsewhere in the Islamic world?  I've seen figures for Iran, where that is also true, and it's clear in Islamic literature that cousin marriages are favored. Consider, for instance, the farmer who understands the speech of animals in an early story in the 1001 nights, where the fact that his wife is his cousin is clearly seen as a plus.

I thanked him for this:

Thanks, that perhaps explains why pushback against modernity is common in the Moslem world. It is an interesting contrast to Christianity where rules against incest were expanded to cousins for a time (unless you paid the Pope). …

Whether it had much to do with indulgences, there is no doubt that Europe freed itself from the inbreeding which, I’ve argued, was crucial in the development and maintenance of human social behaviour. But human behaviour had recently (on an evolutionary timescale) changed to feature larger culture-based groups (see What is Culture for). At times the inbred extended family groups continued within the larger groups, as we see in the Middle East now. In Europe now we see the opposite, with random marriages meaning there is no genetically coherent groups within the culture based groups. This has immediate advantages in strengthening the culture-based group, as we see in the very coherent European nation states that conquered much of the world in the 19th Century, but there are long term costs.

It changes the evolutionary incentives. Opposition to non-cooperating individuals has a cost. And now there is no direct advantage to an individual’s genes to take those actions. With that opposition weakened, the proportion of people not cooperating will rise. Indeed it will continue to rise until that culture-based group starts to malfunction. It might get to the point of losing in struggles with groups which include those extended family subgroups. But perhaps it doesn’t get that far. Perhaps as society gets dysfunctional, with lots of bad guys causing trouble, then there is incentive for families to try to hang together via cousin marriages.

So we might reasonably expect an oscillation between inbreeding with extended family groups, and outbreeding with individual loyalty going directly to the culture-based group.

I believe that cousin marriages and extended families creates a very conservative environment. In particular they have to suppress individual freedom to prevent random marriages. Freedom and individual initiative has been the most powerful advantage of the West in recent times, and very likely for other successful culture-based groups in the past. But the disadvantage will eventually catch up with us, if we let it.