The genome of four skeletons, 8,000 and 3,000 years old, sheds light on the history of Homo sapiens in Africa.
Researchers at Harvard University have reconstructed the genomes of four skeletons dating back 8,000 and 3,000 years. The study allows researchers to outline, for the first time, different patterns of dispersal and differentiation across sub-Saharan Africa.
Published in the journal Nature, this research is the result of a multidisciplinary and international collaboration involving researchers from the Université libre de Bruxelles, the Royal Museum for Central Africa in Tervuren, the Royal Belgian Institute of Natural Sciences, and the University of Yaoundé I.
A Crucial Site
The story begins in the 1990s at the Shum Laka site, near the city of Bamenda in northwestern Cameroon. This 1,200 m² rock shelter is nestled behind a waterfall, at an altitude of 1,600 m on the slope of a volcano. The site is crucial for understanding African history: it is in this region that the origin of all Bantu-speaking peoples is located. They are believed to have left it more than 3,000 years ago, migrating as far as South Africa. Yet, at the time, the area was virtually unknown archaeologically.
Pierre de Maret, a professor at the Free University of Brussels, directed the excavations at the Shum Laka site, in collaboration with Els Cornelissen of the Royal Museum for Central Africa in Tervuren and Raymond Assombang of the University of Yaoundé. Between 1991 and 1994, researchers unearthed the oldest human remains available in this pivotal area between West and Central Africa: 18 human skeletons, belonging to two groups of burials, one dated to approximately 8,000 years ago, the other to 3,000.
DNA from four skeletons
“It was interesting to try to recover DNA from these skeletons and to successfully reconstruct their genomes, both to discover which present-day populations they might be the ancestors of, and to identify any possible links between these two groups of burials,” explains Pierre de Maret, CReA-Patrimoine, Faculty of Philosophy and Social Sciences, Université libre de Bruxelles. However, DNA is difficult to preserve in a hot and humid environment, such as this region of Africa. After several unsuccessful attempts, a team from Harvard University nevertheless succeeded in reconstructing the complete genome of four of these skeletons, two dated to 8,000 years ago, and two to 3,000 years ago.
Continuity in the Occupation of the Region
The two oldest skeletons, which had been buried one on top of the other, are those of a male child of approximately four years old and an adolescent of about 15 years old. They appear to be fourth-degree relatives. Researchers discovered that the adolescent has an extremely rare A00 haplotype on his Y chromosome, currently found only in the same region of Africa. This is the first time it has been found in ancient DNA.
The two more recent skeletons are those of a boy of about eight years old and a girl of about four years old. They are second-degree relatives, meaning they are either uncle/niece or aunt/nephew. Although separated by nearly 5,000 years, the genomes of these four individuals are very similar, indicating remarkable continuity in the occupation of the region.
Surprise: Close to the Pygmies of Central Africa
The researchers then compared this genetic data with that available for different populations across sub-Saharan Africa. “Surprisingly, these four genomes are much closer to those of other hunter-gatherers in Central Africa (Pygmies) than to Bantu farming populations. Genetically, these four individuals are close to the ancient population base of West Africa and, at the same time, but to a lesser extent, to the ancestors of the ‘Pygmy’ hunter-gatherers of Central Africa,” notes Pierre de Maret.
Published in the January 22nd issue of Nature, this study is invaluable: it allows researchers to outline, for the first time, different patterns of dispersal and differentiation into four main population lineages across sub-Saharan Africa. The study brought together 33 authors from 8 different countries and multiple disciplines.
The archaeological excavations were supported by the FNRS, the MRAC and the ULB.