The misery of diversity?

I just finished reading this 2024 NBER Working Paper by Resul Cesur (University of Connecticut) and Sadullah Yıldırım (Marmara University), provocatively titled "The Misery of Diversity". They look at whether greater genetic diversity is associated with subjective wellbeing (SWB, measured as happiness, or life satisfaction, or affect balance), and find that:

...diversity lowers human SWB, measured by cognitive life evaluations and hedonic assessments of emotional states.

Cesur and Yıldırım demonstrate these results using data on genetic diversity that comes from this 2013 article by Ashraf and Galor (ungated version here). As Cesur and Yıldırım explain:

Population geneticists demonstrate that the dispersal of anatomically modern humans via migratory routes determined within-ethnic genetic heterogeneity. As one moves away from Ethiopia via migratory tracts, genetic diversity, defined as the likelihood of two randomly picked individuals having dissimilar genetic material, decreases...

Our diversity measure impacts the outcomes of interest through social ecology, which, over many generations, likely has influenced cultural evolution. In particular, interpersonal diversity determines the endowment of genetic variation, a measure of social diversity, capturing within-group interpersonal differences across the globe...

This measure of social diversity performs better than conventional diversity indicators, such as the indices of fractionalization and polarization, in capturing the true extent of diversity... In particular, these authors show that while interpersonal population diversity has a substantial and precisely estimated impact on intrastate conflict, fractionalization, and polarization indices fail to explain it.

Underlying data for this index is the expected heterozygosity measures of 53 indigenous human populations genotyped at 780 microsatellite loci as a part of the Human Genome Diversity Project (HGDP–CEPH). It captures the probability that two randomly selected individuals within an ethnic group differ in genetic makeup. In light of the Out of Africa hypothesis, Ashraf and Galor (2013a) constructed predicted genetic diversity for each country by using the coefficient estimate of the impact of migratory distance to Addis Ababa on genetic diversity in the sample of indigenous ethnic groups across the world. Although

Using this measure, with an instrumental variables analysis, Cesur and Yıldırım show that genetic diversity causally decreases subjective wellbeing at both the country level and the individual level (using data from the World Values Survey and the World Happiness Report). Their results are robust to excluding countries that experienced large migrations after 1500 (such as countries in North America and Oceania), and to various other modelling choices. Cesur and Yıldırım dig into the mechanisms for lower subjective wellbeing, and conclude that:

...the misery of diversity is an evolutionary trap caused by the mismatch it creates between the ancestral and current social environments via reduced social cohesion, retarded state capacity, elevated mistrust, and increased inequality of economic opportunities.

So, it seems like this is good evidence that genetic diversity decreases subjective wellbeing. However, there are a couple of problems. First, when most people think about diversity, they are thinking about between-group diversity, not within-group diversity. Between-group diversity is what you get when people from different ethnic groups are together. Within-group diversity is what you get when people from the same ethnic group differ genetically from each other. Cesur and Yıldırım's measure is heavily weighted towards within-group diversity. And indeed, in one of their analyses they find that it is within-group diversity that matters the most in their analysis. When they split their measure into within-group and between-group diversity, within-group diversity has a statistically significant (and negative) effect on subjective wellbeing measures, while between-group diversity is statistically significant.

So, Cesur and Yıldırım's analysis might be correct, but at the same time kind of misses the point. Between-group diversity is something that has potential policy levers (migration policy), whereas within-group genetic diversity is not something that is amenable to policy change. At least, not without eugenics (and, to be clear, I am not advocating for that). 

The second problem comes from the analysis of first-generation and second-generation immigrants in Europe and the US, where Cesur and Yıldırım find that:

...while home country diversity continues to hurt the SWB of first-generation immigrants, such effects weaken among the second-generation, suggesting that long-run improvements in the social environment can mitigate the misery of diversity over generations.

These results are not well-explained. If a person is born in one country, and then moves to a new country, shouldn't it matter how long they are exposed to the genetic diversity in the country of birth, and how long they are exposed to the genetic diversity in the destination country, in terms of the impact on subjective wellbeing? Cesur and Yıldırım don't show any dose-response relationship here. And there should be no effects at all on the second generation (which is what they find), because for the second-generation immigrants, the genetic diversity they have been exposed to is the country of their own birth, not the country of birth of their parents. However, that is only a small problem in an otherwise interesting paper.

Overall, I think Cesur and Yıldırım need to engage a bit more with why anyone should care about genetic diversity, given that it is not amenable to policy change. Until they can do that, this paper can be filed under the interesting, but unhelpful category.

[HT: Marginal Revolution, last year]