In the rainforests of Africa, being small is so helpful that it evolved twice in separate groups.
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.
鈥淚n both groups, there was greater variation in those regions associated with being short, but no overlap between them,鈥� says Barreiro. This suggests they evolved their stature independently instead of inheriting the same 鈥減ygmy genes鈥� from a common ancestor.
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Pygmyism clearly offered an evolutionary advantage, says Barreiro. He thinks it might be because pygmies tend to live almost exclusively in the dense rainforest. 鈥淚f you鈥檙e short, you find it much easier because you鈥檙e bending much less to duck under branches,鈥� says Barreiro. His team followed pygmies in forests in the Philippines and Uganda. 鈥淭he shorter ones bend over less, sweat less and thereby expend less energy.鈥�
Or it could be that rainforests are so dangerous that people need to reach sexual maturity earlier to be sure of reproducing, says of Erasmus University Medical Center in Rotterdam, the Netherlands. That would cause them to stop growing earlier, reducing average height.
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