Article Summary: “The Out of Africa Hypothesis” by Ashraf & Galor


Title: The Out of Africa Hypothesis: Human Genetic Diversity and Comparative Economic Development
Author: Quamrul Ashraf and Oded Galor
Scope: 4 stars
Readability: 2 stars
My personal rating: 4 stars
See more on my book rating system.

Topic of Article

The authors explore the effects of early human migration out of Africa had on genetic diversity and economic development.

My Comment

I am not sure that I agree with the author’s hypothesis, but I do find it interesting. One should never discount a biological explanation for human behavior just because it makes us uncomfortable. I believe, however, that geography gives a much better explanation of differing levels of economic development than genetics.

Key Take-aways

  • Early humans migrated from Africa in successive migrations. Humans gradually settled the rest of world in with small groups migrating past the frontier with each generation.
  • Each of these small groups that was relatively homogenous genetically.
  • The result was high levels of genetic diversity in Sub-Saharan Africa with much lower levels of diversity in the rest of the world. The further the distance from Sub-Saharan Africa along land routes, the lower the levels of genetic diversity within the population.
  • The authors believe that higher levels of genetic diversity leads to a greater diversity of ideas, but lower levels of the ability to cooperate in large groups. Lower levels of genetic diversity leads to greater cooperation, but fewer new ideas.
  • The authors believe that nations with medium levels of genetic diversity lead to greater levels of economic development because they acquire enough new ideas and they can still cooperate.

Important Quotes from Article

This research advances and empirically establishes the hypothesis that, in the course of the prehistoric exodus of Homo sapiens out of Africa, variation in migratory distance to various settlements across the globe affected genetic diversity and has had a persistent hump-shaped effect on comparative economic development, reflecting the trade-off between the beneficial and the detrimental effects of diversity on productivity. While the low diversity of Native American populations and the high diversity of African populations have been detrimental for the development of these regions, the intermediate levels of diversity associated with European and Asian populations have been conducive for development.

This research argues that deep-rooted factors, determined tens of thousands of years ago, have had a significant effect on the process of economic development from the dawn of humankind to the contemporary era. It advances the hypothesis that, in the course of the exodus of Homo sapiens out of Africa, variation in migratory distance from the cradle of humankind in East Africa to various settlements across the globe affected genetic diversity and has had a long-lasting hump-shaped effect on the pattern of comparative economic development that is not captured by geographical, institutional, and cultural factors.

Consistent with the predictions of the theory, the empirical analysis finds that the level of genetic diversity within a society has a hump-shaped effect on development outcomes in the precolonial as well as in the modern era, reflecting the trade-off between the beneficial and the detrimental effects of diversity on productivity. While 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, the intermediate levels of genetic diversity prevalent among European and Asian populations have been conducive for development. This research thus highlights one of the deepest channels in comparative development, pertaining not to factors associated with the onset of complex agricultural societies as in the influential hypothesis of Diamond (1997), but to conditions innately related to the very dawn of humankind itself.

The hypothesis rests upon two fundamental building blocks. First, migratory distance from the cradle of humankind in East Africa had an adverse effect on the degree of genetic diversity within ancient indigenous settlements across the globe.

Following the prevailing hypothesis, commonly known as the serial founder effect.

Second, there exists an optimal level of diversity for each stage of economic development, reflecting the interplay between the opposing effects of diversity on the development process. The adverse effect pertains to the detrimental impact of diversity on the efficiency of the aggregate production process. Heterogeneity raises the likelihood of disarray and mistrust, reducing cooperation and disrupting the socioeconomic order. Higher diversity is therefore associated with lower productivity, which inhibits the capacity of the economy to operate efficiently relative to its production possibility frontier. The beneficial effect of diversity, on the other hand, concerns the positive role of heterogeneity in the expansion of society’s production possibility frontier. A wider spectrum of traits is more likely to contain those that are complementary to the advancement and successful implementation of superior technological paradigms. Higher diversity therefore enhances society’s capability to integrate advanced and more efficient production methods, expanding the economy’s production possibility frontier and conferring the benefits of improved productivity.

The main results from the historical analysis, employing predicted genetic diversity in the extended sample of countries, indicate that, controlling for the influence of land productivity, the timing of the Neolithic Revolution, and continent fixed effects, a 1 percentage point increase in diversity for the most homogenous society in the sample would raise its population density in 1500 ce by 36 percent, whereas a 1 percentage point decrease in diversity for the most diverse society would raise its population density by 29 percent. Further, a 1 percentage point change in diversity in either direction at the predicted optimum of 0.683 would lower population density by 1.5 percent.

The partial R2 associated with diversity suggests that residual genetic diversity explains about 16 percent of the cross-country variation in residual log income per capita in 2000 ce, conditional on the institutional, cultural, and geographical covariates in the baseline regression model.

Genetic diversity is negatively associated with the extent of cooperative behavior, as measured by the prevalence of interpersonal trust, and positively associated with innovative activity, as measured by the intensity of scientific knowledge creation.

Migratory distance from East Africa has an adverse linear effect on genetic diversity. They interpret this finding as providing support for a serial founder effect originating in East Africa, reflecting a process where the populating of the world occurred in a series of discrete steps involving subgroups leaving initial settlements to establish new settlements farther away and carrying with them only a subset of the overall genetic diversity of their parental colonies.

The empirical analysis of Ramachandran et al. (2005) establishes migratory distance from East Africa as a strong negative predictor of genetic diversity at the ethnic group level. Based on the R 2 of their regression, migratory distance alone explains almost 86 percent of the cross-group variation in within-group diversity.

Moreover, the agricultural transition timing and land productivity channels independently explain 54 percent and 57 percent of the limited cross-country sample variation in log population density in 1500 ce.

By exploiting the combined explanatory power of all 3 channels, the estimated model explains an impressive 89 percent of the limited-sample cross-country variation in log population density.

The partial R 2 associated with genetic diversity suggests that residual genetic diversity explains about 16 percent of the cross-country variation in residual log income per capita in 2000 ce, conditional on the covariates from the baseline regression model.

The coefficients associated with the diversity channel in column 5 imply that (i) increasing the diversity of the most homogenous country in the sample (Bolivia) by 1 percentage point would raise its income per capita in the year 2000 ce by 41 percent; (ii) decreasing the diversity of the most diverse country in the sample (Ethiopia) by 1 percentage point would raise its income per capita by 21 percent; (iii) a 1 percentage point change in genetic diversity (in either direction) at the optimum level of 0.721 (that most closely resembles the diversity level of the United States) would lower income per capita by 1.9 percent; (iv) increasing the diversity of Bolivia to the level prevalent in the United States would increase Bolivia’s per capita income by a factor of 5.4, closing the income gap between the two countries from a ratio of 12:1 to 2.2:1; and (v) decreasing the diversity of Ethiopia to the level prevalent in the United States would increase Ethiopia’s per capita income by a factor of 1.7 and thus close the income gap between the two countries from a ratio of 47:1 to 27:1.

The hump-shaped effect of genetic diversity remains highly significant and the optimal diversity estimate remains virtually intact if the sample is restricted to (i) non-OECD economies (i.e., economies that were less attractive to migrants) in column 2; (ii) non–Neo-European countries (i.e., excluding the United States, Canada, Australia, and New Zealand) in column 3; (iii) non–Latin American countries in column 4; (iv) non–sub-Saharan African countries in column 5; and (v) countries for which the indigenous population is larger than 97 percent of the entire population.

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