Africa’s oldest human DNA reveals ancient social networks

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Genetic analysis of ancient African skeletons has sequenced an 18,000-year-old human genome, providing clues to how the continent’s ancient occupants lived, traveled and reproduced.

In the review Naturethe researchers explain that the first African populations began to form large social networks around 50,000 years ago, but became more fragmented around the time of the last glacial maximum.

Archaeological evidence suggests that ancient Africans began trading obsidian and other symbolic objects 300,000 years ago, but it was not until the late Stone Age that long-lasting trade distance have really intensified. Researchers have often speculated that this transfer of goods may go hand in hand with the movement of people, but the scarcity of genetic samples has made this theory impossible to confirm.

Generally, DNA cannot survive for long periods of time in Africa’s hot, humid climate, and researchers had never managed to sequence a human genome from sub-Saharan Africa older than 9,000 years. However, the authors of this latest study recovered genetic material from six individuals buried in Malawi, Tanzania and Zambia who lived between 5,000 and 18,000 years ago.

They also reviewed the records of 28 previously reported individuals recovered from burial sites across the continent, generating enhanced genetic data for 15 of them. After analyzing the DNA, the researchers found that these 34 individuals were descended from three separate source populations originating in northeast, central and southern Africa.

This implies that the continent was once inhabited by three distinct groups, which must have remained disconnected from each other for long periods. However, the mixing of these three lineages at each burial site indicates that an exchange of genetic information between the three populations began sometime before 20,000 years ago.

According to the study authors, this process likely began around 50,000 years ago, as it was around this time that the archaeological record began to show an increase in the movement of goods over long distances. As trading networks spread across the continent, it seems likely that people also started having children with partners from distant regions.

However, genetic data also reveals that this long-distance DNA exchange has decreased significantly since about 20,000 years ago, indicating that people started interbreeding with their close neighbors from that time. According to the study authors, this period coincides with the last glacial maximum, when climate change may have restricted the movement of people and forced populations to become more sedentary.

“Initially, people found reproductive mates across wide geographic and cultural pools,” study author Jessica Thompson explained in an article. declaration. “Later, they prioritized partners who lived closer and were potentially more culturally similar.”

“It may be because at that time, previously established social networks allowed the flow of information and technology without people having to travel,” adds co-author Elizabeth Sawchuk.

Importantly, the discovery of such ancient DNA in sub-Saharan Africa allows researchers to confirm some widely disputed hypotheses regarding how and when the continent’s ancient inhabitants began to travel long distances to find mates.

Previously, archaeologists had to rely on material artefacts to theorize about social networks that may have existed across the continent, but the addition of genetic data allows scientists to paint a stronger picture.

“It’s been difficult to piece together events from our deep past using the DNA of people living today, and artifacts like stone tools and beads can’t tell us the whole story,” Sawchuck said. . “Ancient DNA provides direct insight into people themselves, which was the missing piece of the puzzle.”

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