For decades, scientists who studied early modern humans thought that our ancestors initially inhabited only small areas of Africa, the savannas of the continent’s east and south, before moving north to Asia, Europe and beyond. According to this theory, early humans bypassed West and Central Africa, particularly the rainforests. These regions, they believe, were populated much later.
But now a growing group of researchers is challenging that narrative. In Senegal, Cameroon, Malawi and elsewhere, they have uncovered evidence that early humans spread across much of Africa before venturing elsewhere. This work has moved the field beyond the old narrative of arrival outside Africa and is transforming our understanding of how multiple groups of modern humans mixed and spread across the continent, offering a more nuanced picture of the complex origins of our species.
“It’s becoming increasingly clear that humans didn’t come from a single population in a single region of Africa,” says Eleanor Scerri, an archaeologist at the Max Planck Institute for Geoanthropology in Jena, Germany. “If we really want to understand human evolution, we need to study the entire African continent.”
Most researchers agree that the first modern humans appeared in Africa between 200,000 and 300,000 years ago. About 60,000 years ago, they spread to other parts of the world. Until recently, however, most experts believed that these humans only populated West and Central Africa, particularly the rainforests, in the last 20,000 years or so.
To some researchers, that narrative made little sense. “Humans like to move around a lot,” says Sarah Tishkoff, a geneticist at the University of Pennsylvania who has spent more than two decades trying to untangle Africa’s deep genetic lineage. “They had this beautiful continent, they could move all over the place, go to different niches, with different resources.”
The reason no one has found evidence of ancient human settlement in West and Central Africa is because few researchers have been interested in it. For decades, most researchers have tended to focus on areas of the continent where fieldwork is less challenging. East and Southern Africa have a drier, cooler climate and more open terrain, making fossils easier to find and date. Much of West and Central Africa is hot and humid, so bones and DNA degrade more quickly. And the region can be a difficult place to work, not only because much of it is covered in dense forests, but also because some areas are plagued by chaotic, long-running conflicts.
Some research suggests that cultural biases may also have played a role. “Most of the research has been conducted by people from the global North,” says Jessica Thompson, a paleoanthropologist at Yale University. “And their perspective is, ‘We want to know how people got out of Africa to where we came from.’”
Because of all these factors, most scientists have focused primarily on sites in South and East Africa. This has contributed to the idea that early modern humans primarily inhabited these regions. Frustrated that academics were not taking their ideas seriously, a few researchers began trying to uncover evidence that supported their views. Over the past decade, they have found it.
Last year, a group of scientists from Senegal, Europe and the United States reported that modern humans had lived at a site on the Senegalese coast 150,000 years ago. Previous estimates put the first human habitation in West Africa at 30,000 years ago.
What’s more, the site was in a mangrove forest, rather than a grassland or sparse savannah, as is typical for early humans. Scerri says her latest research in Senegal, not yet published, could push that date back even further. “It’s clear that there were different people in different places, doing different things,” she says. “And they were there for a long time. Much longer than we thought.”
Another study, from 2022, analyzed DNA from the bones of 34 people who lived in sub-Saharan Africa between 5,000 and 18,000 years ago. Examining such ancient DNA is important because it provides a much clearer window into the structure of older African populations. The research showed that between 80,000 and 20,000 years ago, populations that had been relatively isolated from each other began to interact across vast swaths of the continent. These connections stretched thousands of miles, from Ethiopia to South Africa to the forests of central Africa.
“People were clearly moving across vast areas across Africa,” says Thompson, one of the study’s co-authors. “They weren’t staying in these small, isolated populations.”
A study published four years ago in the journal Nature examined the remains of two children found in a rock shelter in Cameroon, in the western part of central Africa. One of the children lived 3,000 years ago, while the other lived 8,000 years ago. The researchers, from Harvard and other institutions, managed to collect DNA from the two children — the first ancient human DNA ever sequenced in central Africa. They detected four distinct human lineages between 60,000 and 80,000 years ago, including a previously unknown lineage — what they called a “ghost population” — that likely lived in West Africa. The findings support the idea that humans have been present in West Africa for much longer than previously thought, and add to the evidence that humanity’s roots extend to more than one region of Africa.
Experts point out that it is important to note that modern humans’ close relatives — Neanderthals, Homo erectus and several other species — had already spread beyond Africa to Europe and Asia, in some cases millions of years ago. But these groups contributed relatively little to the modern human lineage.
Because fossils and ancient DNA can be difficult to find in many parts of Africa, scientists have had to develop innovative approaches to establish the existence of early human habitation. For example, Thompson and his colleagues studied sediments around Lake Malawi in the northern part of the country. Over thousands of years, the lake shrank and grew, depending on the amount of rainfall. During wetter periods, the number of trees around the lake increased dramatically.
But Thompson found that during a wetter period that began 80,000 years ago (and continues today), the number of trees didn’t increase as much as expected. Instead, scientists found an abundance of charcoal. Thompson says this shows that humans were living in the area, perhaps in fairly large numbers, and burning wood on a large scale, either to modify the environment for hunting, cooking, or warmth, or all three.
The Pan-African hypothesis is a key aspect of this new understanding: Scerri and others argue that modern humans likely evolved from the mixing of different groups from different parts of the continent. “There were a number of modern human populations living in different parts of Africa, and we emerged over time from the complex interactions between them,” Scerri says. “Basically, we are a mixture of a mixture of a mixture of a mixture.”
In a study published last year, Brenna Henn, a population geneticist at the University of California, Davis, and her colleagues examined the genomes of nearly 300 Africans from across the continent. By analyzing and comparing the genetic data, they were able to build a model of how humans originated on the continent over the past few hundred thousand years. They found that modern humans descended from at least two distinct populations that lived in different parts of the continent. Henn and her colleagues are now analyzing the genomes of 3,000 people, mostly Africans but also people of African descent who live elsewhere, as well as Native Americans and others.
Scerri also found evidence to support the Pan-African idea. She showed that the Middle Stone Age culture persisted in West Africa until relatively recently, less than 11,000 years ago. This culture, which made stone tools, disappeared much earlier in other parts of the continent, 30,000 to 50,000 years ago. This is important, she says, because it is precisely what Pan-African theory predicts: “In this model, you would expect each region to have its own cultural trajectory, due to periods of isolation. This research shows how that was possible.”
Not everyone is convinced. Richard Klein, a paleoanthropologist at Stanford University who has spent decades studying the origins and migrations of modern humans in Africa, says, “I don’t understand the evolutionary mechanism behind” the pan-African origins theory.
Pontus Skoglund, a population geneticist at the Francis Crick Institute in London who collaborated with Scerri, says the pan-African idea is plausible, but he is not entirely convinced. “It also seems possible to me that a lot of the ancestry of people today could be found in a single region,” he says. “But we don’t know.” He adds that there is still “a lot of uncertainty” about who was where and when.
Scerri acknowledges that more research is needed. But after years of battling skepticism, she feels empowered that this new perspective has caught on. “It’s an exciting field to be working in right now,” she says. “It’s really an incredible story that’s unfolding before our eyes.”
.jpg)
.webp)
0 Comments