But now a growing number of researchers are questioning this theory. Researchers working in Senegal, Cameroon, Malawi and elsewhere are finding evidence that early humans spread across much of Africa before venturing elsewhere. This work is moving the field beyond the traditional African origin theory, transforming our understanding of how multiple groups of early modern humans mixed and spread across the continent, and providing a more nuanced picture of human origins.
“It’s becoming increasingly clear that humans didn’t start out as a single group in one part of Africa,” says archaeologist Eleanor Cheri of the Max Planck Institute for Geoanthropology in Jena, Germany. “If we really want to understand human evolution, we need to look at the whole continent.”
Most researchers agree that early modern humans emerged in Africa 200,000 to 300,000 years ago. About 60,000 years ago, they spread to other parts of the world. But until recently, most experts thought that these humans only inhabited West and Central Africa, particularly its rainforests, for the last 20,000 years or so.
For some researchers, this story makes little sense. “Humans like to move around a lot,” says Sarah Tishkoff, a geneticist at the University of Pennsylvania who has spent more than 20 years working to unravel Africa’s deep genetic lineages. “We had this beautiful continent, and we could move around, and go to different niches with different resources.”
The lack of evidence of early human settlement in West and Central Africa is because so few people have looked there, Seri and his team say. For decades, most researchers have tended to focus on the low-hanging fruit: parts of the continent where fieldwork isn’t too difficult. East and Southern Africa have dry, cool climates and open terrain, making it easy to find and date fossils. Most of West and Central Africa is hot and humid, which causes bones and DNA to deteriorate more quickly. What’s more, the region can be difficult to study, not only because much of it is densely forested, but also because some areas are embroiled in long-term, chaotic conflicts.
Some studies suggest cultural bias may have played a role, too. “Most of the research has been led by people from the Northern Hemisphere,” says Yale paleoanthropologist Jessica Thompson. “Their perspective is, ‘I want to know how people got out of Africa, and where our ancestors are.'”
As a result of all these factors, most scientists have focused primarily on archaeological sites in South and East Africa. This has contributed to the idea that early modern humans lived primarily in these regions. Frustrated that the academic community did not take their ideas seriously, several researchers began trying to find evidence to support their view. Over the past decade or so, they have found evidence.
Last year, a group including scientists from Senegal, Europe and the United States report Modern humans have been found living on the coast of Senegal for 150,000 years, up from previous estimates that the earliest known human habitation in West Africa was 30,000 years ago.
What’s more, the site was in mangrove forest, not the grasslands or sparse savannas typically associated with early human habitation. Seri says that his latest research in Senegal (not yet published) could push the date back even further. “It’s clear that different people were doing different things in different places,” he says. “And they were there for a long time – much longer than we realized.”
another studyA study from 2022 analyzed DNA from the bones of 34 individuals who lived across sub-Saharan Africa between 5,000 and 18,000 years ago. Studying such ancient DNA is important because it gives us a clearer understanding of more ancient African population structure. The study found that between 80,000 and 20,000 years ago, populations that had been fairly isolated from each other began to interact across a wide swath of the African continent. These connections stretched across thousands of miles, from Ethiopia through the forests of Central Africa to South Africa.
“People were clearly moving widely across Africa,” said Thompson, one of the study’s co-authors. “They weren’t staying in small, isolated groups.”
and A paper published in Nature four years ago Researchers from Harvard University and other institutes examined the remains of two children found in a rock shelter in Cameroon, west of Central Africa. One lived 3,000 years ago, the other 8,000 years ago. Researchers from Harvard University and other institutes managed to extract DNA from the two individuals, the first ancient human DNA sequenced from Central Africa. The researchers detected four distinct human lineages dating back 60,000 to 80,000 years, including a previously unknown lineage that probably lived in West Africa (which they call a “ghost population”). The findings further support the idea that humans have been in West Africa for much longer than previously thought, and add to the evidence that our roots are spread across multiple regions of Africa.
Experts say it’s important to note that our closest relatives — Neanderthals, Homo erectus and several others — had already spread beyond Africa into Europe and Asia, in some cases millions of years ago, but these groups contributed relatively little DNA to the modern human lineage.
Because it is so difficult to find fossils or recover ancient DNA in many parts of Africa, scientists have had to develop innovative approaches to uncover early human habitats. For example, Thompson and her colleagues Sediments studied Trees growing around a lake in northern Malawi. For thousands of years, the lake has shrunk and expanded depending on the amount of rainfall. During periods of heavy rainfall, the number of trees growing around the lake increases significantly.
But Thompson found that during the wetter period that began 80,000 years ago (and continues today), tree numbers didn’t increase as much as expected. Instead, scientists found an abundance of charcoal. Thompson says this indicates that there was probably a fairly large human population in the region, who burned wood on a fairly large scale, either to modify the environment for hunting, or for cooking and warmth, or all three.
A key aspect of this new understanding is the Pan-African hypothesis. Seri and his colleagues argue that modern humans probably evolved from a mix of different populations in different parts of the African continent. “There were many modern human populations living in different parts of Africa, and we emerged over time from complex interactions between them,” Seri says. “Essentially, we’re a mix of different populations…
in A study published last yearPopulation geneticist Brenna Henn of the University of California, Davis, and her colleagues have looked at the genomes of about 300 Africans from across the continent. By analyzing and comparing genetic data, they were able to build a model of how humans originated on the African continent over the past hundreds of thousands of years. They found that modern humans descended from at least two different populations, living in different parts of the continent. She and her colleagues are currently analyzing the genomes of 3,000 individuals, most of whom are Africans, but also people of African descent living in other regions, as well as Native Americans.
Seri also found evidence to support the Pan-African idea. He found that a Middle Stone Age culture survived in West Africa very recently, until about 11,000 years ago. This culture – and its particular way of making stone tools – disappeared in other parts of the continent much earlier, between 30,000 and 50,000 years ago. This is important, Seri says, because it is exactly what the Pan-African idea predicts. “In this model, you would expect that, because of periods of isolation, each region would follow its own cultural trajectory. This study shows why that was possible.”
Not everyone is convinced. “The evolutionary mechanisms behind a Pan-African origin are hard to understand,” says Richard Klein, a paleoanthropologist at Stanford University who has studied the origins and migration of early modern humans in Africa for decades.
Pontus Skoglund, a population geneticist at the Francis Crick Institute in London and a collaborator with Sheri, says the Pan-African hypothesis seems plausible but he’s not entirely convinced. “It seems to me possible that most of the ancestors of modern humans were in a single area,” he says. “But we don’t know.” He says there’s still “a lot of uncertainty” about who was where and when.
Seri agrees that more research is needed, but after battling years of skepticism, she feels vindicated by the acceptance of a new perspective. “This is a very exciting area of research right now,” she says. “This is a really incredible story, and it’s unfolding before our eyes.”
