Abstract:
Archaeological findings, numerical human dispersal models and genome analyses suggest several time
windows in the past 200 kyr (thousands of years ago) when anatomically modern humans (AMH)
dispersed out of Africa into the Levant and/or Arabia. From close to the key hominin site of Omo-Kibish,
we provide near continuous proxy evidence for environmental changes in lake sediment cores from the
Chew Bahir basin, south Ethiopia. The data show highly variable hydroclimate conditions from 116 to 66
kyr BP with rapid shifts from very wet to extreme aridity. The wet phases coincide with the timing of the
North African Humid Periods during MIS5, as defined by Nile discharge records from the eastern
Mediterranean. The subsequent record at Chew Bahir suggests stable regional hydrological setting between
58 and 32 kyr (MIS4 and 3), which facilitated the development of more habitable ecosystems,
albeit in generally dry climatic conditions. This shift, from more to less variable hydroclimate, may help
account for the timing of later dispersal events of AMH out of Africa.
