'Huge surprise' reveals how some humans left Africa 50,000 years ago

Before modern humans began their major dispersal out of Africa about 50,000 years ago, they moved to places that were significantly more ecologically diverse, which may have given them the flexibility they needed to migrate across the globe, a new study finds.

Our species, Homo sapiens, originated in Africa more than 300,000 years ago. Genetic evidence suggests that all modern human populations outside Africa mostly descend from a small group of modern humans who started migrating out of Africa about 50,000 years ago.

However, previous research suggests the first waves of Homo sapiens began leaving Africa as early as about 270,000 years ago. This raises the question of why these earlier migration waves left no genetic traces in modern human populations outside Africa today.

In the new study, published Wednesday (June 18) in the journal Nature, researchers analyzed evidence from archaeological sites across Africa dated to between 120,000 to 14,000 years ago. By examining ancient plant and animal remains, the scientists reconstructed what kinds of habitats and climates people lived in across that span of time — this painted a picture of the vegetation, temperatures and rainfall a given area might have had.

The researchers discovered that modern humans began to expand the range of habitat types in which they lived starting about 70,000 years ago — they went into forests in West and Central Africa, deserts in North Africa, and places with greater ranges of annual temperatures.

"Humans have been successfully living in challenging habitats for at least 70,000 years," study co-lead author Emily Hallett, an archaeologist at Loyola University Chicago, told Live Science.

Related: When did Homo sapiens first appear?

This discovery "was a huge surprise" and sheds light on why the last major dispersal of modern humans from Africa proved successful, study co-senior author Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute of Geoanthropology in Germany, told Live Science.

"Our ecological flexibility is part of what enabled our species to disperse across the globe and thrive in each habitat we encountered," Hallett said.

Modern humans were pretty good generalists from the very beginning, inhabiting a wide range of habitats, noted study co-senior author Andrea Manica, an evolutionary ecologist at the University of Cambridge.

"What we see about 70,000 years ago is Homo sapiens becoming the ultimate generalist, and pushing into more and more extreme environments," Manica told Live Science. "That newly found additional flexibility gave them an edge 50,000 years ago, allowing them to spread rapidly across the whole globe, and thriving in environments that were novel and sometimes very challenging, such as those found at very northern latitudes."

The greater ecological flexibility the researchers saw in modern humans was likely not the result of a single evolutionary adaptation or technological innovation, said study co-lead author Michela Leonardi, an evolutionary biologist at the University of Cambridge. Instead, it looks more like the complex interaction of many factors, such as modern human populations living across larger ranges, experiencing greater levels of contact and cultural exchanges between groups, "and a higher likelihood of developing and maintaining innovations," she told Live Science.

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Before a successful dispersal out of Africa about 50,000 years ago, ancient humans learned how to thrive in a variety of African environments.

Starting around 70,000 years ago, ancient humans learned how to adapt to new and different environments in Africa. This knowledge and adaptability likely helped them as they later dispersed into Eurasia.

A present-day photo of coastline in Kariba, Zimbabwe. Previous dispersals out of Africa failed, but a new study suggests that once our species learned how to adapt to new environments, that helped them successfully leave the continent.

These new findings may shed light not just on the journey of modern humans out of Africa, but human evolution in general, including ancient lineages in the genus Homo like Homo erectus and the closest extinct relatives of modern humans, the Neanderthals and Denisovans, said William E. Banks, an archaeologist at the French National Center for Scientific Research who did not take part in this study but wrote an editorial about it, which was also published in the journal Nature on June 18.

"Earlier members of our genus must have also expanded the range of environmental conditions that they occupied when they left Africa and began to permanently occupy regions of Eurasia," Banks told Live Science.

It remains uncertain why modern humans began expanding to more challenging habitats about 70,000 years ago, Scerri said. One possibility is that the spaces in which they had lived were shrinking, although it's unknown why at this point — "it was likely out of necessity," she said.

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