Saturday, April 18, 2009
Genetics of pygmy evolution in Africa
Some of you might be interested in a recent study about the evolutionary origins of African human pygmy populations, which is discussed in this bloggpost. A recent study have investigated the molecular genetic history of African pygmy populations and concluded that they are not secondarily derived from the farming populations of the Bantu people. Instead, the different and the isolated pygmy populations in the African rainforests are historical relicts of a greater contiguous population of an ancestral hunter-gather society that was split up in to different fragmented populations when the African Bantu people expanded about 10 000 years ago.
The different pygmy populations in Africa have thus not evolved their short body stature in parallel. Rather their phenotypic traits are traits that they inherited from their ancestors. The pygmy populations and the Bantu people have been separated for at least 60 000 years. The agricultural revolution took place the last 10 000 years, and when the Bantu people brought agriculture to sub-saharan Africa, their population sizes exploded. This is because the carrying capacity of agricultural populations is considerably higher than for hunter-gather societies. which is not very surprising. After all, by using agriculture you can feed a much larger population per unit area than you could by hunting.
The pygmies were thus marginalized by the rapidly expanding Bantu-farmers, and their once large population was split up in to several smaller fragmented populations. The once more widespread pygmies are today more less isolated from each other in the deep African rainforest.
As an aside, this is an interesting example of how population genetics, particularly the use of the population genetic software STRUCTURE, can be fruitfully used to infer population histories and population genetic parameters (see figure above). This is something we are also working on in our laboratory, particularly Anna in her studies of Mediterranean Podarcis-lizards.