What phenomenon enabled the demographic growth of Bantu farmers in Africa and led to their genetic differentiation from the Pygmy hunter-gatherer communities?
Up to now, scientists thought that the emergence of agriculture on the continent 5,000 years ago played a major role. But an international team, including an IRD researcher, has revealed that the history of these peoples was played out long before. According to an extensive genomic study, the two types of population result from tens of thousands of years of adaptation to their different environments. However, the demographic boom the ancestors of the Bantus dates back to between 7,000 to 10,000 years ago, which might call into question the impact of agriculture, which emerged more than 2,000 years later.
Agriculture, a trigger element in history?
Agriculture has been a major technological cultural and environmental revolution for humanity. Particularly in Central Africa, where it has fundamentally changed the landscapes and livelihoods of sub-Saharan populations since it emerged there 5,000 years ago. He was hitherto recognised that the development of this practice, thanks to the abundance of the resources created, had enabled the demographic and geographical growth of the population having adopted it, which was later known as “Bantus” in Africa. This farming people would then have gradually differentiated genetically from the pygmy hunter-gatherers communities living in forests. A genomic study, published in the Nature Communications journal, has just challenged this assumption.
Much older events
This work, conducted in Central Africa, reveals a very different scenario: the genetic differentiation between the Pygmies and the ancestors of the Bantus, and the demographic growth of the latter, occurred long before the advent of agriculture on the continent. The researchers analysed the genomes of more than 300 people, half of them village farmers and the other half Pygmies. It is apparent that the genetic differentiation of the two populations proves to be ancient and is the result of tens of thousands of years of adaptation to their different environments. In addition, the ancestors of the Bantus experienced very strong growth of their populations between 7,000 and 10,000 years ago, or more than 2,000 years before the emergence of agriculture. This demographic boom forced them to cultivate the land to provide for their needs, and not the other way around.
Belated yet intense exchanges
Another lesson learned from this study: genetic mixing between the two societies did indeed take place at some point in the evolution, but it happened much later than scientists believed, less than 1,000 years ago, despite the contacts which Pygmies and Bantus have maintained for 5,000 years. The fact that these two populations coexisted for 4,000 years without mixing genetically reflects their specific socio-economic structures and the special status that the Pygmies have long had in the eyes of their contemporaries. However, over the last thousand years, this mixing took place in an intense way: the genomes of the Pygmy communities today have up to 50% of the genetic material inherited from their farmer neighbours.
By questioning the impact of the discovery of agriculture on the history of genetics and demographics in Africa, this work highlights a major question: what phenomenon allowed the development of the ancestors of the Bantus? Researchers are now exploring environmental factors.
Institut de Recherche pour le Développement (IRD)
