Genetic structure in African populations: implications for human demographic history

Abstract

The continent of Africa is the source of all anatomically modern humans that dispersed across the planet during the past 100,000 years. As such, African populations are characterized by high genetic diversity and low levels of linkage disequilibrium (LD) among loci, as compared to populations from other continents. African populations also possess a number of genetic adaptations that have evolved in response to the diverse climates, diets, geographic environments, and infectious agents that characterize the African continent. Recently, Tishkoff et al. (2009) performed a genome-wide analysis of substructure based on DNA from 2432 Africans from 121 geographically diverse populations. The authors analyzed patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers and identified 14 ancestral population clusters that correlate well with self-described ethnicity and shared cultural or linguistic properties. The results suggest that African populations may have maintained a large and subdivided population structure throughout much of their evolutionary history. In this chapter, we synthesize recent work documenting evidence of African population structure and discuss the implications for inferences about evolutionary history in both African populations and anatomically modern humans as a whole.

Figure 1

Extreme models of population structure within Africa. (Vertical lines) African lineages, (black lines) lineages that have survived to the present day, (gray lines) lineages that have not survived. (A) The first model is analogous to the multiregional model of global human origins. Under this model, hominid populations existed in relative isolation across Africa for most of their histories and evolved independently into anatomically modern humans (AMH). Horizontal arrows indicate low levels of migration between the longstructured populations. (B) The second model is analogous to the recentorigin model of global human origins. Under this model, archaic hominids across Africa were completely replaced with AMH, which then became structured only recently.