Southern Ethiopia


How climate change may have shaped humanity’s migration across Earth

University of Hull scientist Dr Jonathan Dean has joined a team of international experts to explore how climate change may have impacted humanity’s migration across Earth.

Homo sapiens – our species – are thought to have evolved in eastern Africa sometime before 200,000 years ago.

Reconstructions have now shown how climate in eastern Africa has evolved over the last 200,000 years, and could have enabled the migration of humankind out of the continent and across the planet.

The team of scientists, including Dr Dean, examined hundreds of metres of sediment cores drilled into the bed of a lake called Chew Bahir in southern Ethiopia.

They were then able to work out how the climate changed going back through time.

Dr Dean said: “We’ve always wanted to know how climate changed in the region where Homo sapiens evolved, so we can work out whether climate change could have influenced the course of human history.

“But until recently there haven’t been any records of climate change that spanned the entire history of our species. Our long record of climate change has been years in the making.

“While working at the University of Hull, I have collaborated with the British Geological Survey to analyse some of the data for this study.”

The research team found that from 200,000 to 125,000 years ago, the climate of eastern Africa was relatively wet, with at least 20–30% more precipitation than the region receives today, meaning conditions were favourable for the early humans with plenty of food and water.

Further studies have shown wet conditions in other parts of Africa at this time. Under such conditions, humans could move relatively easily through Africa. Some even ventured out of Africa to reach the Arabian Peninsula, which they did well before 100,000 years ago.

However, it does appear that these intrepid humans died out before they could disperse further.

Then, from 125,000 years ago, the climate gradually became drier in eastern Africa. This long-term drying trend was interrupted by short-lived climate shifts that lasted a few thousand years.

These have been linked to changes in the circulation of the North Atlantic Ocean, showing how changes in one part of the world can impact upon the climate in another.

One of these short-lived climate shifts was a wet period that occurred 62,000–60,000 years ago.

This roughly coincides with the occurrence of the ‘successful’ out-of-Africa migration of Homo sapiens – the one that went on to populate the rest of the world.

This wet period would have made the out of Africa migration possible by providing sufficient food and water resources for the humans to survive the long journey.

Over the past 60,000 years, the conditions became increasingly challenging for the humans who stayed in eastern Africa.

There were some particularly dry intervals where Chew Bahir even completely dried out. At these times, humans had to seek refuge at higher elevations in Ethiopia, where they could still access sufficient food and water.

The full paper is available here.

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