Economic mobility and reproductive success

Tyler Cowen writes:

How much of immobility is due to “inherited talent plus diminishing role for random circumstance”?  Is not this cause of immobility very different — both practically and morally — from such factors as discrimination, bad schools, occupational licensing, etc.?  What are you supposed to get when you combine genetics with meritocracy?

I have  written before about how decreased social mobility may be a sign of equalised opportunity. In a perfect meritocracy, assortment will largely be through genes.

However, there can still be social mobility even though assortment is through genetic factors. This is through differential reproductive success. If an economic class has  more children, many of those children move up or down the social scale as there is no longer room for them in their cohort.

This social mobility can have some interesting effects. If, for example, the bottom 80 per cent of the economic distribution has much higher fertility than the top 20 per cent, some of those born in the bottom 80 per cent will move into the top  quintile. If those who move up the scale do not experience any increase in income (as their productivity has not increased, only their prevalence has changed), the relative wealth of those born to someone from the initial top 20 per cent may increase. Social mobility appears to increase inequality through concentrating wealth in the less fertile top.

Greg Clark describes the converse situation in A Farewell to Alms. In pre-Industrial Revolution England, the rich had higher reproductive success. There was necessarily downward social mobility. Over time, the population became largely composed of those from the top. Productivity increased among the lower classes, but many of them weren’t from the lower classes at all.