A climatic context for the out-of-Africa migration

Around 200,000 yr ago, Homo sapiens emerged in Africa. By 40 ka, Homo sapiens had spread throughout Eurasia, and a major competing species, the Neanderthals, became extinct. The factors that drove our species "out of Africa" remain a topic of vigorous debate. Existing research invokes climate change as either providing opportunities or imposing limits on human migration. Yet the paleoclimate history of northeast Africa, the gateway to migration, is unknown. Here, we reconstruct temperature and aridity in the Horn of Africa region spanning the past 200,000 yr. Our data suggest that warm and wet conditions from 120,000 to 90,000 yr ago could have facilitated early waves of human migration toward the Levant and Arabia, as supported by fossil and lithic evidence. However, the primary out-of-Africa event, as constrained by genetic studies (ca. 65-55 ka), occurred during a cold and dry time. This complicates the climatemigration relationship, suggesting that both "push" and "pull" factors may have prompted Homo sapiens to colonize Eurasia.