non-African lineages derive from a subset of these African lineages (Cann et al., 1987; Ingman et al., 2000; Underhill et al., 2001; Gonder et al., 2007; Tishkoff et al., 2007a; Behar et al., 2008; Henn et al., 2008). Consistent with the archaeological record, estimates of the time to the most recent ancestor (TMRCA) for the mtDNA lineages give an age range of ~200–100 kya (Ingman et al., 2000; Salas et al., 2002; Tang et al., 2002; Behar et al., 2008) and similar results have been published for NRY lineages, ~200–65 kya (Scozzari et al., 1999; Underhill et al., 2000; Tang et al., 2002). Therefore, the genetic data corroborate a model in which modern humans arose in Africa 200–100 kya and subsequently, one or more populations split off and migrated out of Africa. The migration out of Africa was accompanied by a population bottleneck, which resulted in a reduction in genetic diversity in non-African populations relative to Africans (Campbell and Tishkoff, 2008).
The Middle Stone Age, which took place ~250–40 kya (Henshilwood et al., 2002), is a period in the archaeological record that indicates a significant change in culture and subsistence technology in Africa. Several sites in eastern, central, and southern Africa contain artifacts consistent with a shift in technology and population expansion ~75–55 kya, including hunting weapons, indications of increased plant utilization, signs of increased marine exploitation, and evidence of large-scale movement of red ochre (used for art), stone, and shell ornaments (McBrearty and Brooks, 2000; Henshilwood et al., 2001, 2002; Mellars, 2006). It is tempting to speculate that these developments are tied to improvements in human communication; however, the reconstruction of proto-languages does not extend back this far in time; therefore, there is no empirical way to establish when or where human language emerged. Interestingly, an analysis of mtDNA data estimates a population expansion in Africa 70 kya (Excoffier and Schneider, 1999), consistent with the archaeological evidence from the late Middle Stone Age. Furthermore, we would not expect to see the same signal of expansion in non-African populations given that the extreme bottleneck associated with the migration out of Africa most likely obscures more ancient demographic signals.
The Neolithic period, beginning ~10 kya, included the development of agriculture and animal domestication in Africa, with concomitant changes in population demographics due to population growth and migration to new regions. Below we discuss several such movements including