Robin Hanson says that people would rather live like ‘foragers’ than like ‘farmers’:

I think a lot of today’s political disputes come down to a conflict between farmer and forager ways, with forager ways slowly and steadily winning out since the industrial revolution. It seems we acted like farmers when farming required that, but when richer we feel we can afford to revert to more natural-feeling forager ways. The main exceptions, like school and workplace domination and ranking, are required to generate industry-level wealth. We live a farmer lifestyle when poor, but prefer to buy a forager lifestyle when rich.

In other words, in a situation of contact between traditional cultures heavily adapted to vertical transmission and progressive cultures heavily adapted to horizontal transmission such that it’s possible for people to convert from the former to the latter, the latter will win out.

This situation of contact exists in the case of religious groups like the Haredi Jews and the Amish, but the retention rates of at least the latter (I haven’t looked into Haredi retention rate) have gone up over time.

The historical evidence shows a decline in defection in some Amish communities in the last half of the twentieth century. Defection in Geauga County, Ohio, for example, dropped from 30 percent for those born during the 1920s to 5 percent for those born in the 1960s. Similarly, the exit of people from the Elkhart-LaGrange community in northern Indiana dipped from 21 percent for those born in the 1930s to 10 percent for those born in the 1950s. The loss of Amish-born people in Nappanee, Indiana, dropped from 55 percent in the 1920s to 16 percent in the 1970s.

How can this be explained? Cochran and Harpending attribute it to genetic selection: if there’s a genetic component to the plain, ‘farming’ personality that the choice to join the Amish church selects for (and they think there is), then, each generation, you get biological evaporative cooling: the people with the lowest ‘Amish quotient’ leave, and its average across the group increases.

The key assumption here is that personality has a genetic component. If you grant that, everything else falls into place.

Let’s say a space alien lands in Belgium and redesigns all its buildings overnight, so that the buildings in the north of Belgium are designed for very tall people, the buildings in the south of Belgium are designed for very short people, and the buildings in the middle of Belgium are designed for people of average height. (To avoid the issues posed by sex differences in height, let’s also say the alien converts all of Belgium to Islam, adds separate men’s and women’s facilities to every building, and carries out the height calculations separately for each sex.) If you’re a very tall person living in the south or the middle of Belgium, you’ll get sick of having to duck all the time and move north; if you’re a very short person living in the north or the middle of Belgium, you’ll get sick of being unable to reach things and move south. Everyone knows that there’s a genetic component to height – so everyone would expect that, after a few decades of this, there would be a genetic height gradient in Belgium. It might take a few generations – you could have people who didn’t eat well in their childhood moving south and having tall children – but it would eventually show up.

There wouldn’t be a genetic height gradient in Belgium now, but that’s because the selection mechanism isn’t there. To step out of the analogy: if your social context is uniform in ‘farming’/‘foraging’ tendencies, your genetic tendency toward one or the other won’t matter for the purposes of selection. It’s only when you have ‘farming’ and ‘foraging’ populations in close contact that the selection would apply – and the strength of the effect is going to depend on how easy it is to move from one to the other.

Strictly speaking, no genetic explanation is necessary. If the fertility and retention rates of a group are high enough, the group will grow over time – and the group doesn’t even have to grow; it just has to decline at a lower rate than the general population for it to show proportional growth. And since retention rates can, for whatever reason, increase over time, it’s even possible for a declining group to turn around, as long as its fertility rate is far enough above replacement to allow it.

Anything that causes higher fertility is selected for, and anything that causes lower fertility is selected against. This is the principle behind IQ shredders. In this case, if ‘farming’/‘foraging’ tendencies have a significant genetic component, there’s a ‘foraging’ shredder: the exodus from ‘farming’ to ‘foraging’ social contexts is not a time-invariant law about the relative strength of the two memeplexes or of horizontal to vertical transmission – it’s a temporary process of selection. The ‘farmers’ burn off their ‘foragers’, but they have more children, so they win in the end.