Wednesday, 5 February 2014
Scientists say they may be able to fill a blank in the history of central Africa's hunter-gatherers, whose past is one of the most elusive of any community in the world.
At a key period in the human odyssey, these hunter-gatherer tribes —sometimes referred to as pygmies — shunned interbreeding with Bantu-speaking communities who were early farmers, according to a gene analysis.
The two groups first met when the Bantu groups, having acquired farming technology some 5000 years ago, started moving out of the region of Nigeria and Cameroon into eastern, central and southern Africa.
Most of the other hunter-gatherers they encountered soon adopted the agricultural, sedentary lifestyle and even the languages of the Bantu groups.
But a few populations, like those of the central African rainforest, kept their traditional, mobile way of life.
The central African hunter-gatherers may have traded pottery, tools and ideas with the newcomers, but not their genes, according to the study in the journal Nature Communications.
The evidence comes from a reading of the DNA of some 300 individuals — hunter-gathers and Bantu-speakers from Gabon, Cameroon, Uganda, the Central African Republic and the Democratic Republic of Congo.
"This result suggests that social relations established since the two groups first met were quickly followed by a strong taboo against inter-marriage that is to some extent still observed today," says co-author Etienne Patin, a geneticist at France's Institut Pasteur.
"Anthropological research has suggested that the taboo may have something to do with the image the villagers have of pygmies as the custodians of forest magic, but also disapproval of their way of life" as mobile hunter gatherers, he adds.
It was not clear why the taboo seems to have been partly lifted about a thousand years ago.
The pattern observed in central Africa was very different to what happened in the south of the continent, where the conquering farmers' encounters with San hunter-gatherers "resulted in immediate genetic exchanges", according to the study.
Previous research had shown that the common ancestor of the central African hunter-gathers and Bantu farmers lived about 60,000 to 70,000 years ago.
The two groups spent tens of thousands of years adapting to their different environments before meeting up again.
The latest findings challenge the accepted science that genetic diversity is closely correlated with geographic distance between human groups.
The central African hunter-gathers are a case in point — there are only about 200,000 individuals in total, yet their genetic diversity far exceeds that of their sedentary neighbours, the researchers write.
The Batwa people of Uganda, for example, are genetically quite distinct from the Mbuti people who live a mere 500 kilometres away in the Democratic Republic of Congo.
The researchers further found that the hunter-gather genome could contain as much as 50 per cent DNA inherited from people of Bantu origin.
And their height is directly proportional to the amount of Bantu DNA inherited — "the less one is 'pygmy', genetically speaking, the taller one is," says Patin.http://www.abc.net.au/science/articles/2014/02/05/3938817.htm