The Out of Africa Hypothesis of Comparative Development
This research avenue has explored the persistent effect of the prehistoric exodus of Homo sapiens from Africa on the composition of human traits within human populations and, thus, on comparative economic development across societies from the dawn of civilization to the contemporary era. In particular, this line of research has advanced the hypothesis and empirically established that migratory distances from the cradle of mankind in East Africa to the indigenous settlements of the ancestral populations of nations or ethnic groups negatively affected their levels of popuation diversity and, thereby, generated a persistent hump-shaped influence on development outcomes, reflecting the fundamental trade-off between the beneficial and detrimental effects of diversity on productivity at the societal level (Ashraf and Galor, AER 2013; Ashraf, Galor and Klemp, 2014, Ashraf, Galor and Klemp, 2018).
Although diversity diminishes interpersonal trust, cooperation, and economic coordination, adversely affecting the productivity of society, complementarity across diverse productive traits stimulates innovations and gains from specialization, thus contributing to society's economic performance. In the presence of diminishing marginal returns to diversity and homogeneity, the aggregate productivity of ethnic groups, countries, or regions that are characterized by intermediate levels of diversity is therefore expected to be higher than that associated with excessively homogenous or heterogeneous societies.
Consistent with the fundamental elements of this hypothesis, interpersonal population diversity has been established as a central determinant of observed ethnic and cultural heterogeneity, as reflected by the number of ethnic groups and the degree of ethnolinguistic fractionalization in a society (Ashraf and Galor, 2013, AER PP, 2013), and as a major force in the emergence of civil conflicts (Arbatl, Ashraf, Galor and Klemp, Econometrica, 2019). Interpersonal population diversity has also been shown to contribute to diminished interpersonal trust and more intensive innovative activity (Ashraf and Galor, AER 2013), as well as greater occupational heterogeneity and gains from specialization (Depetris-Chauvin and Ozak, 2018). Moreover, it has been argued that population diversity has shaped the nature of both precolonial and contemporary political institutions. In particular, although diversity triggered the development of institutions for mitigating the adverse influence of diversity on social cohesion, the contribution of diversity to economic inequality and class stratication ultimately led to the formation and persistence of extractive and autocratic institutions (Galor and Klemp, 2018).