Humans Migrated Out of Africa Thanks to Climate Change

Researchers are taking a closer look at human migration out of Africa. They've examined two predominant hypotheses concerning the timing of this migration, and have found that one comes out on top.

There are two main scenarios for human migration out of Africa. The first is that human populations expanded rapidly from Africa to southern Asia via the coastlines of Arabia about 50,000 to 60,000 years ago. The second theory suggests that dispersal into the Arabian interior began much earlier-around 75,000 top 130,000 years ago. This spread occurred during multiple phases when increased rainfall provided sufficient freshwater to support expanding populations.

In order to see which theory might win out, the researchers examined an alluvial fan aggradation record from southeast Arabia spanning the past 160,000 years. Situated along the proposed southern dispersal route, the Al Sibetah alluvial fan sequence provides a record of landscape change in southeast Arabia. More specifically, it reveals that there were multiple humid episodes during both glacial and interglacial periods.

The alluvial fan sequence actually indicates that increased monsoon rainfall led to the widespread activation of drainage systems and grassland development throughout regions that were important for the dispersal of early human populations. This, in turn, supports the latter theory.

"The dispersal of early human populations out of Africa is dynamically linked with the changing climate and environmental conditions of Arabia," said Ash Parton, one of the researchers, in a news release. "Although now arid, at times the vast Arabian deserts were transformed into landscapes littered with freshwater lakes and active river systems. Such episodes of dramatically increased rainfall were the result of the intensification and northward displacement of the Indian Ocean Monsoon, which caused rainfall to reach across much of the Arabian Peninsula."

The findings provide support for the theory that climate change allowed for a series of migrations. This, in turn, reveals a bit more about our ancient ancestors and how humans first dispersed out of Africa.

The findings are published in the journal Geology.

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