A new study by geoscientists and climatologists provides evidence that summer monsoons from Asia and Africa may have reached into the Middle East for periods of time going back at least 125,000 years, providing suitable corridors for human migration.

The finding suggested that modern humans, who originated in Africa, began migrating out of the continent at least 40,000 years earlier than scientists previously thought.

But the story of how and when modern humans originated and spread throughout the world is still in draft form. That’s because science hasn’t settled how many times modern humans left Africa, or just how many routes they may have taken.

A new study published this week [Nov. 25, 2019] in the Proceedings of the National Academy of Sciences by American and Israeli geoscientists and climatologists provides evidence that summer monsoons from Asia and Africa may have reached into the Middle East for periods of time going back at least 125,000 years, providing suitable corridors for human migration.

The likely timing of these northward monsoon expansions corresponds with cyclical changes in Earth’s orbit that would have brought the Northern Hemisphere closer to the sun and led to increased summer precipitation. With increased summer precipitation there may have been increased vegetation, supporting animal and human migration into the region.

«It could be important context for experts studying how, why, and when early modern humans were migrating out of Africa,» says lead author Ian Orland, a University of Wisconsin-Madison geoscientist now at the Wisconsin Geological and Natural History Survey, in the Division of Extension. «The Eastern Mediterranean was a critical bottleneck for that route out of Africa and if our suggestion is right, at 125,000 years ago and potentially at other periods, there may have been more consistent rainfall on a year-round basis that might enhance the ability of humans to migrate.»

For as long as humans have kept records, winters have been wet and summers have been hot and dry in the Levant, a region that includes Israel, Syria, Lebanon, Jordan and Palestine. Before modern times, those hot, dry summers would have presented a significant barrier to people trying to move across the landscape.

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