Gregory Nemec
Long ago, in the shadow of great stones in northern Malawi, hunter-gatherers often stopped for a rest. They might bring their kill under shelter, make a meal over a fire, or even bury their dead, a practice that has made possible one of the largest analyses of ancient DNA in Africa. That work was published recently in Nature by assistant professor of anthropology Jessica Thompson and her colleagues. One of the people they unearthed, in a Malawi rock shelter, had died 16,000 years ago—providing some of the oldest DNA ever sequenced from the African continent. Along with DNA from 33 other people found buried across Africa, it has given researchers a snapshot of the movements of hunter-gatherers who lived in the Late Stone Age, before the rise of agriculture.
Sequencing DNA from burials has helped scientists study long-ago human populations, particularly in Europe, where studies of DNA revealed the ebb and flow of ancient migrations. That led, Thompson says, to the genesis of her project: “I was just so jealous that we didn’t have similar access to even that type of data anywhere in Africa.” In hot climates, DNA breaks down easily, and some colleagues were skeptical that Thompson could get enough of it to analyze. But she persisted, and in the end, with new biotechnology techniques, the team succeeded.
The DNA of each human individual is an amalgam of their ancestors’ genomes, mixed together over the generations. When Thompson and her collaborators looked at DNA from the 34 African burials, some of which have been held in museums and repositories for decades, they could see that these people’s forebears were from many different regions of Africa and had intermingled over time. Curiously, comparing these earlier genomes to those of modern-day inhabitants showed a stark difference. “Most people don’t have any of this type of ancestry at all,” says Thompson. The researchers believe that this is because the modern-day populations are descendants of farmers who eventually took over the area, pushing the foragers out: “They overwrote genetically this whole ancient [population structure] that was here for 50,000 years,” Thompson says.
The DNA also showed that while the ancestral heritage of the 34 people had come from many distant regions, their families had looked for mates close to home. DNA analyses of individuals who were found even a relatively small distance apart showed very little relationship to each other. That illuminates a pattern archaeologists have noticed: artifacts from far-off cultures show up among the belongings of the ancient foragers, which indicates the existence of trade. But although goods traveled vast distances, the DNA suggests that people didn’t, or at least didn’t travel to find partners.
Thompson has her eye on other sites in Malawi—and on earlier eras. “We’re moving to another site that has deposits that date back at least 30,000 years. We will be excavating there over the summer,” she says. “I’m very interested in going back deeper in time.”
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