In the rainforests of Africa, being small is so helpful that it evolved twice in separate groups. Luis Barreiro of the University of Montreal in Quebec, Canada, and his colleagues identified 16 regions of the genome associated with short stature in the Batwa pygmies of Uganda. They then compared these regions in 169 Batwa and 74 Baka pygmies from West Africa. "In both groups, there was greater variation in those regions associated with being short, but no overlap between them," says Barreiro.
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