Genes shed light on pygmy history


Scientists have been able to fill in a blank in the history of Central Africa’s pygmies, whose past is one of the most elusive of any community in the world.

At a key period in human migration, these hunter-gatherer tribes shunned interbreeding with Bantu-speaking farming communities, according to a new gene analysis.

The two groups first met when the Bantu groups, having acquired farming technology some 5,000 years earlier, started moving out of the region around Nigeria and Cameroon into Eastern, Central and Southern Africa. Most of the other hunter-gatherers they encountered soon adopted the sedentary agricultural lifestyle and even the languages of the Bantu groups.

But a few populations, like the pygmies of the Central African rain forest, kept their mobile way of life. The pygmies may have traded pottery, tools and ideas with the newcomers, but not their genes, said the study, which appeared in the journal Nature Communications.

The evidence cited in the study comes from DNA readings of some 300 individuals — pygmies 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 intermarriage that is to some extent still observed today,” said co-author Etienne Patin, a geneticist at France’s Pasteur Institute. “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.

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 from what happened in the south of the continent, where the conquering farmers’ encounters with San hunter-gatherers “resulted in immediate genetic exchanges,” said the study.

Previous research had shown that the common ancestor of the pygmies 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 scientific consensus that genetic diversity is closely correlated with geographic distance between human groups.

The Central African pygmies are a case in point. There are only about 200,000 individuals in total, yet their genetic diversity far exceeds that of their sedentary neighbors, said the study.

The Batwa pygmies of Uganda, for example, are genetically quite distinct from the Mbuti pygmies who live a mere 500 km away in Congo.

The researchers further found that DNA inherited from people of Bantu origin could make up as much as 50 percent of the pygmy genome.

Pygmies’ height, the study also found, is proportional to the amount of nonpygmy DNA inherited — “the less one is pygmy, genetically speaking, the taller one is,” Patin said.