Sharing ideas might have helped Homo sapiens adapt for life outside Africa

Scientists have taken a step forward in understanding how our species survived outside Africa.

While Homo sapiens made multiple journeys out of Africa over a period of more than 200,000 years, only one migration around 50,000 years ago gave rise to all non-African people. Why this migration succeeded where so many others didn’t is one of the greatest questions in human evolution.

New research, published in the journal Nature, may help to solve this age-old puzzle. By combining fossil and environmental data from the past 120,000 years, a team of researchers found that modern humans adapted to a much wider range of environments, known as niches, around 70,000 years ago.

As their ability to survive in an increased number of ecological niches expanded, our species was able to live in forests, savannahs and deserts that were previously inhospitable. Dr Michela Leonardi, one of our scientists who co-led the research, says that this would have helped humans to survive in the world beyond Africa.

“By becoming more flexible to life in a range of environments, our species could expand its range in Africa,” Michela explains. “While we’re not entirely sure why this was happening, it might be related to different African populations increasingly coming into contact and sharing their ideas and strategies to thrive in different environments.”

“Over time, the increased sharing of ideas would help Homo sapiens to expand its range further, and come into contact with even more populations. This feedback loop would have made our species even more versatile, so humans were ready to cope with the challenges they faced outside of Africa when the main migration took place.”

How did our species survive leaving Africa?

Over the past few decades, various explanations have been suggested as to why just one migration of humans out of Africa left direct descendants alive today.

One potential theory was the development of new technologies. Advances leading to more effective weapons or tools could have enabled humans to better find food or create shelter, giving them a better chance of survival as they spread across the world.

Other researchers have suggested that changes in the human brain, and associated shifts in behaviour, might have allowed our species to respond better to the challenges it faced. While all are possibilities, a lack of direct evidence means there’s no single answer.

“Africa’s hot climate means that it can be much harder for genetic evidence or archaeological remains to survive,” Michela explains. “This makes it much more difficult to see why change is taking place, especially across an entire continent.”

What evidence does survive, however, shows that sites with human activity become more widespread across Africa between 125,000-50,000 years ago. At the same time, the archaeological record starts to become more similar, suggesting that our species was becoming more homogenous.

Together, this suggests that growing populations seem to have been moving into new environments as the pressure for resources grew.

To take a closer look at what was happening, the team turned to an approach Michela had developed to see how animals like the aurochs reacted to environmental change following the last Ice Age. It uses climate reconstructions to plot where species could theoretically have lived, and combines that with archaeological evidence to see if they started to use these new habitats.

By applying this to signs of human occupation in Africa between 120,000 to 14,000 years ago, the team could see how our species was adapting to life in new environments.

Where did Homo sapiens live before leaving Africa?

The researchers’ simulations show that the geographic range of Homo sapiens began to expand from around 70,000 years ago, particularly in western, central and northern Africa.

As the overall area of forests, deserts and savannah stayed relatively constant over this time, it suggests that the range of our species expanded not because our preferred habitat was increasing, but because we got better at living in the more difficult environments.

As different populations of humans were coming in to contact with each other, the researchers suggest that it seems likely these people were sharing the ideas and knowledge of how to survive in these new regions. This first allowed our ancestors to live in the forests of western and central Africa, before moving into the Sahara Desert and its surroundings.

Previous research suggests that, around the same time, modern humans were also starting to eat a wider diet and shape their environment through controlled burns and water storage. While these changes didn’t happen everywhere at once, they provide further evidence that humans were increasingly adaptable to their environment.

The peak of our species’ niche expansion was reached around 50,000 years ago, coinciding with the out of Africa migration. Professor Andrea Manica, a co-author from the University of Cambridge, describes this as a “key result”.

“We know that humans probably dispersed into Eurasia several times based on fossil evidence,” Andrea explains. “Previously, they seem to have done so during particularly favourable windows of increased rainfall in the Sahara and Arabian Deserts, which created ‘green corridors’ for people to move into Eurasia.”

“Between 70,000 to 50,000 years ago, however, the easiest route out of Africa would have been more challenging than during previous periods. Yet, this expansion was sizeable and ultimate successful.”

Having shown that Homo sapiens was living in new environments, the team also hope to see how else humans were changing at the time.

“Our future research is looking into the cultural, morphological and genetic changes that took place in Africa, and how they link to the population changes taking place at the time,” Michela says. “It’s not a simple process, but it will take us another step closer to understanding our evolution in Africa.”