Hat tip to Christine Kenneally who pointed out this research on climate change, “East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins,” published in PNAS. This is excellent research that comes right on the coat tails of this recent post.

Christopher Scholz and colleagues studied deep sediment cores from Lake Malawi Bathymetric map of Lake Malawiin Africa and found evidence to suggest that the transition from a long dry period susceptible to extreme drought to a stable, wetter climate may have stimulated the expansion and migration of early human populations.

The authors say that a series of megadroughts occurred in the region around 135,000 to 75,000 years ago and they caused extreme drying of Rift Valley Lakes. During the most severe drought periods, Lake Malawi’s water volume was reduced by at least 95 percent while water levels fell to below 15 percent current levels. Other African lakes dried out completely and populations of African plant and animal populations fluctuated dramatically. The cores show that around 70,000 years ago, the climate stabilized and became much wetter, evidently creating conditions favorable for human populations, which expanded and eventually spread out across the globe. The authors write,

“Such climate change may have stimulated the expansion and migrations of early modern human populations.”

The results appear to support the “Out Of Africa” theory the humans arose in Africa and subsequently colonized the world during one or more migrations rather than the multiregional hypothesis for human evolution.