as populations that speak linguistically similar languages are more likely to exchange genes. The pattern of genetic variation in Africa is also consistent with geographic barriers limiting gene flow as exampled by the geographic/genetic distinction between northern African and sub-Saharan African populations. When we focus, however, on particular exceptions to these broad patterns, we are able to more fully appreciate the complex population histories that have contributed to extant patterns of genetic variation. The development of sequencing and genotyping technologies is advancing at an unprecedented rate and is allowing for the genotyping of millions of single-nucleotide polymorphisms and the sequencing of millions of nucleotides across populations. These data, coupled with computational methods for inferring demographic parameters and testing demographic models (e.g., maximum likelihood and approximate Bayesian computation), are well powered to refine our understanding of African past population histories. The incorporation of archaeological and linguistic data will be important for establishing testable hypotheses and elucidating the evolutionary processes (or forces) that have shaped the genomic landscape in Africa.
We thank Scott Williams, Françoise Friedlaender, William Beggs, Charla Lambert, Joseph Jarvis, Michael Campbell, and the Tishkoff Lab members for support and helpful discussions. This work was funded by National Science Foundation Grants BCS-0196183 and BCS-0827436, National Institutes of Health Grants R01GM076637 and 1R01GM083606–01, and National Institutes of Health Pioneer 1-DP1-OD-006445–01 awards (to S.A.T.).