DOUBLE HELIX DESTINY

THE SOURCE: “The ‘Out of Africa’ Hypothesis, Human Genetic Diversity, and Comparative Economic Development” by Quamrul Ashraf and Oded Galor, in American Economic Review, Feb. 2013.

WHAT GIVES RICH SOCIETIES THEIR MOJO? Scholars who look for the roots of economic development offer an array of answers: Culture, history, or geography push a country toward prosperity, they claim.

Quamrul Ashraf and Oded Galor, economists at Williams College and Brown University, respectively, propose an entirely different explanation: genetic diversity. They say the range of a given population’s genes — determined 70,000 to 90,000 years ago when humans first journeyed out of East Africa — played a decisive role in determining which lands would hit the economic jackpot.

In a process known as the serial founder effect, populations closer (via land migration routes) to modern-day Ethiopia, where the earliest evidence of Homo sapiens has been found, had higher levels of genetic diversity than groups that settled farther away. The nearer societies had more “founders” — or early settlers — and therefore more genetic variation. When smaller groups peeled off and ventured into Europe and Asia, they carried a smaller gene pool with them. It shrank further when humans trekked to the Americas.

This made all the difference. Societies flourish when their populations have just enough genetic diversity, but not too much. (Geneticists gauge genetic diversity with “expected heterozygosity,” which measures the likelihood that two people within a group will have, say, a difference in eye color or some other heritable trait.) Genetically diverse societies are more likely to cook up new technologies; people with varying traits develop different specialties and work in complementary ways.

But heterozygosity comes with tradeoffs. Kin selection theory suggests that the more closely related people are genetically, the more likely they are to cooperate with one another. More diversity equals less cooperation. While spurring innovation and production, genetic diversity simultaneously “raises the likelihood of disarray and mistrust, reducing cooperation and disrupting the socioeconomic order.” On the other end of the spectrum, low genetic diversity promotes high levels of public trust and economic efficiency. Yet the gene pool does not vary enough to kick development into high gear.

Thanks to the path taken by the earliest humans out of Africa, Asian and European populations that developed at least 3,000 miles from humanity’s birthplace hit the diversity sweet spot. In contrast, “the low degree of diversity among Native American populations and the high degree of diversity among African populations have been detrimental forces in the development of these regions,” Ashraf and Galor write.

The authors tested their theory by comparing genetic diversity in select countries with these countries’ level of economic development in 1500, before the influence of colonialism and industrialization was felt, and again in 2000. They used population density as a proxy for wealth in 1500, surveying 21 countries. For 2000, they expanded the sample to include 145 countries and gauged wealth on the basis of income per capita.

When they graphed the data on wealth against genetic diversity, they found what they expected. In 1500, the regions at an intermediate distance from East Africa — Europe and Asia — enjoyed the highest rates of development. African African and American populations lagged behind the boom areas. The pattern persisted in the comparison of per capita incomes of 145 countries in 2000, with countries consisting of large immigrant populations, such as the United States and Canada, joining the advantaged group.

Ashraf and Galor aren’t the first to connect modern wealth disparities to long-ago events. In his 1997 bestseller Guns, Germs, and Steel, Jared Diamond argued that ancient societies blessed by geographic good fortune had a decisive leg up on competitors; they adopted domestic agriculture earlier, cementing dominance that has persisted into contemporary times. Ashraf and Galor accounted for the timing of agricultural adoption in their calculations and found support for Diamond’s idea.

But the correlation between development and genetic diversity is much stronger. Of the 145 nations considered in the 2000 comparison, Bolivia, one of the world’s poorer countries, was the most genetically homogenous. The authors calculated that if Bolivia’s level of genetic diversity were just one percentage point higher, its current per capita income would be 41 percent greater.

Ethiopia, where the first modern humans emerged 150,000 years ago, lies at the other end of the spectrum. There, extreme genetic diversity has led to crippling poverty. A drop in heterozygosity of just one percentage point would result in a 21 percent bump in contemporary income per capita, the authors found.

Ashraf and Galor also calculated a theoretical “optimum” level of genetic diversity at which a country would be most likely to thrive. The optimum level was markedly higher in 2000 than it was in 1500. After the Industrial Revolution, the authors hypothesize, “the beneficial forces associated with greater diversity became intensified in an environment characterized by more rapid technological progress.”

The nation that came closest to the ideal level of post-industrial genetic diversity? According to Ashraf and Galor’s calculations, it was the United States.

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