New Study Provides More Genetic Evidence for Origins of African Pygmies
April 10, 2009
PLoS Genetics tackles this speculation head-on, using a novel and comprehensive approach in unraveling the origins of Pygmies.When examining the origins of a particular group of people, many studies focus on a single part of the human genome; the Y-chromosome for example, or mitochondrial DNA. However, the authors of this study wanted to get a complete picture of the genetic history of the Pygmies, so they looked at 24 separate regions of the human genome. Altogether, the authors examined more than 33,000 letters of DNA for each of the 236 individuals they sampled.After collecting and analyzing DNA samples from several different Pygmy groups, nearby Bantu-speaking farmers and other hunter-gatherer groups, the authors ran more than a million computer simulations on the data they had collected, allowing them to deduce the most likely scenario for how the Pygmies became so genetically distinct.This is the second time in recent months that geneticists have offered an account of Pygmy population history. In February, a paper in Current Biology concluded that western Pygmies began interbreeding with their agricultural neighbors about 2,800 years ago.The new PLoS paper concludes that Pygmies and their neighbors, non-Pygmy African farmers, had been separated for more than 50,000 years before that. They both shared a common genetic ancestor who lived nearly 56,000 years ago at a time when humans were spreading throughout the African continent, settling and thriving in the rainforests, savannahs, and coastal regions. It is also around this time that the first human groups left Africa, journeying into Asia.As these various groups of people began finding their own niches in the diverse African environment, they began to distinguish themselves culturally, physically and genetically. The authors of this study believe that it is from this time onward that the unique physical form of African Pygmies began to evolve.But the computer simulations also revealed much about the genetic diversity of the Pygmies themselves. Pygmies today are generally divided into two ethnic groups: eastern and western. Each has a somewhat different history, culture and genetic signature, though both are relatively similar in stature.The authors believe that it was the environment that led to the separation of these two groups. About 20,000 years ago, the Ice Age was at its peak. As glaciers covered most of northern Europe, and sea levels dropped across the globe, the abundant rainforests of sub-Saharan Africa began to shrink. A once lush and expansive tropical forest was now a series of smaller, drier forests, interspersed with savannah grassland. The growing separation of the forests, the authors propose, led to the growing separation of peoples who had once lived side by side. Various Pygmy groups retreated to isolated pockets of the shrinking forests. By the Ice Age’s peak, the once homogeneous Pygmies had split into two main groups. The computer simulations confirmed the authors’ hypotheses, putting the most likely split at around 21,000 years ago.Today, the western – or Mbenga – Pygmies inhabit the West Congo Basin, while the eastern – or Mbuti – Pygmies, live in the forests of the Democratic Republic of the Congo. And, while each group is short in stature, the past 20,000 years of biological and cultural evolution has made each group unique. This study serves as a reminder of the wealth of history that is housed in our genes, if we only know where to look.