for National Geographic News
Human pygmies around the world are smaller than average because they tend to live very short lives, in some communities as little as 16 years, a new study says.
Such brief life spans have put evolutionary pressure on pygmy women to stop growing and start having babies sooner, the research suggests. The energy that would typically be used for growth is instead expended on reproduction at a younger age.
"The idea is that [pygmies] have to stop growing earlier, because when you start reproducing—at least for women—all the energy you would put in growth is put into reproduction," said Andrea Migliano, the lead author of the study and a postdoctoral fellow at Clare College, Cambridge, in the United Kingdom.
"You have to choose—either you grow or you reproduce," she said.
Evolution, Not Nutrition?
Migliano's paper, published in this week's online edition of the Proceedings of the National Academy of Sciences, challenges the commonly held belief that pygmies' small stature is the result of environmental factors such as poor nutrition.
Migliano said she was suspicious of that idea, because some of the world's tallest people—such as Kenya's Maasai and Samburu—also typically suffer from poor nutrition.
Instead, Migliano suggests, stature is the result of an evolutionary process woven into pygmies' genetic structure and would not change quickly if pygmies were subjected to less stressful environments.
Pygmies are defined as populations with an average male height of less than five feet (one and a half meters). People of that description are found all over the world, from Brazil to Papua New Guinea.
Migliano and her colleagues studied two populations of pygmies in the Philippines, the Aeta and the Batak.
Mortality is high in these communities because the populations are ravaged by easily preventable diseases, such as measles and chicken pox. Their diets are also poor, making them more susceptible to illness, Migliano said.
Migliano's data are partly supported by similar work done by other scientists.
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