Thread by @captgouda24

When states in the US banned cousin marriage, it led to more people immigrating to the cities and changing into higher paying professions. More evidence for how kinship networks hold back development. 1/

It used to be that 7% of marriages were between first cousins in the late 1700s -- this was down to 1.5% in the early 1900s.

People who married their cousins tended to be poorer, more rural, and geographically immobile. The census does not report income, but, we can infer something from the occupation.

If you plot out where cousin marriages occur, it's rural states and the Mormons (who didn't exactly move out there with much variety).

So how do we know if people are cousins? We don't see it directly, but we can infer it from the surnames. If lots of people are marrying with the same name, something's up.

To make a causal argument, we need changes in the legality of cousin marriage. First, bans led to a decrease in cousin marriage in the states

We can't compare outcomes of people in different states. If we expect for there to be convergence to the mean of both development and cousin marriage, this will get confounded. Instead, they compare *surnames*, contrasted by their frequency of cousin marriage.

The surnames with a high frequency of cousin marriage, interacted with the state ban, show that they are more likely to migrate to the cities now --

-- and that their income, proxied by occupational score, rises.

Why? Likely because it breaks down kinship networks. People become more dispersed in space, and family sizes become smaller, driven both by fewer children but also by being less likely to live with other couples.

They're also more likely to be institutionalized, suggesting a weaker link to kin.

Ghosh, Hwang, Squires, "Economic Consequences of Kinship: Evidence from U.S. Bans on Cousin Marriage" (2023)
academic.oup.com/qje/article/13…