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The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early latePleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after Ϸ70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations.human origins ͉ Lake Malawi ͉ paleoclimate ͉ Pleistocene

Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.