Although modern humans left Africa multiple times over 100,000 years ago, those broadly ancestral to non-Africans dispersed less than 100,000 years ago 1 . Most models hold that these events occurred through green corridors created during humid periods because arid intervals constrained population movements 2 . Here we report an archaeological site—Shinfa-Metema 1, in the lowlands of northwest Ethiopia, with Youngest Toba Tuff cryptotephra dated to around 74,000 years ago—that provides early and rare evidence of intensive riverine-based foraging aided by the likely adoption of the bow and arrow. The diet included a wide range of terrestrial and aquatic animals. Stable oxygen isotopes from fossil mammal teeth and ostrich eggshell show that the site was occupied during a period of high seasonal aridity. The unusual abundance of fish suggests that capture occurred in the ever smaller and shallower waterholes of a seasonal river during a long dry season, revealing flexible adaptations to challenging climatic conditions during the Middle Stone Age. Adaptive foraging along dry-season waterholes would have transformed seasonal rivers into ‘blue highway’ corridors, potentially facilitating an out-of-Africa dispersal and suggesting that the event was not restricted to times of humid climates. The behavioural flexibility required to survive seasonally arid conditions in general, and the apparent short-term effects of the Toba supereruption in particular were probably key to the most recent dispersal and subsequent worldwide expansion of modern humans.
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