High School Genetic Diversity and Later-life Student Outcomes: Micro-level Evidence from the Wisconsin Longitudinal Study. C. Justin Cook, Jason M. Fletcher. http://www.nber.org/papers/w23520

Abstract: A novel hypothesis posits that levels of genetic diversity in a population may partially explain variation in the development and success of countries. Our paper extends evidence on this novel question by subjecting the hypothesis to an alternative context that eliminates many alternative hypotheses by aggregating representative data to the high school level from a single state (Wisconsin) in 1957, when the population was composed nearly entirely of individuals of European ancestry. Using this sample of high school aggregations, we too find a strong effect of genetic diversity on socioeconomic outcomes. Additionally, we check an existing mechanism and propose a new potential mechanism of the results for innovation: personality traits associated with creativity and divergent thinking.

NBER Working Paper No. 23520
NBER Program(s):   EFG   LS

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But these authors find worse results:
Ethnic and linguistic fractionalization contributes to poverty levels
Ethnic Diversity and Poverty. By Sefa Awawory Churchill, Russell Smyth
https://doi.org/10.1016/j.worlddev.2017.02.032
World Development, Volume 95, July 2017, Pages 285–302

Maybe it is a case of both trends at the same time...