Did invading farmers drive pygmy diversity?
By Ewen Callaway West African pygmy populations vary more than their similarities in body size would indicate. A new genetic analysis of pygmy populations native to Gabon and Cameroon suggests they split apart from one another roughly 3000 years ago and from other humans at least 50,000 years ago. European explorers first encountered pygmy populations in the 19th century and lumped them together under a name that Homer used in the Iliad to describe an African tribe of diminutive crane-fighters. “Artificially we created a common origin and a common heritage just by the use of this pygmy term,” says Paul Verdu, a geneticist at the Musée de l’Homme in Paris, who led the study Although pygmies resemble one another in physical stature – about 1.5 metres on average – they share little else in common. Some live as jungle hunter-gatherers, while others practice agriculture and commerce and live in the savannah. Many of their languages are also very varied, and the populations do not view identify any of the others as an ancestral group. “There is no such thing as a pygmy civilisation or identity,” Verdu says. Working with ethnographers, anthropologists and musicologists, his team collected DNA from 604 people belonging to nine pygmy groups and 12 non-pygmy populations living nearby. Their analysis of 28 DNA markers hinted at close relations among the non-pygmies, but more widespread genetic diversity among pygmies. A mathematical analysis of the data suggested that the pygmy populations diverged from one another roughly 2,800 years ago. What’s more, all the pygmy populations showed signs of inbreeding with outsiders. None of the non-pygmy populations, however, exhibited any evidence of pygmy genes. This apparent paradox might be explained by widespread discrimination against pygmies, Verdu says. Occasionally, pygmy women marry into non-pygmy families and have children. Often these women and children are treated as second-class citizens and they eventually return to their native lands. Exactly why pygmy populations diverged from one another is unclear, Verdu says. He hypothesises that an ancient migration of farmers and herdsmen across sub-Saharan Africa – dubbed the Bantu expansion – might have segmented pygmies living in West Africa. “That makes sense to me,” says Sarah Tishkoff, a geneticist at the University of Pennsylvania in Philadelphia, who was not involved in the study. “You’ve got these Bantu people coming through and maybe that caused isolation among these hunter gatherers who would have otherwise roamed freely.” A bigger mystery for Tishkoff is the relationship between West African pygmies and East African pygmies, who live thousands of kilometres away. Journal reference: Current Biology (DOI: 10.1016/j.cub.20812.049) More on these topics: