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Why Pygmies Are So Short, a Study

Aug 19, 2014 10:39 AM EDT

It may be one of the last examples of ongoing natural selection in humans. Pygmy hunter-gatherer tribes in Uganda have genes to thank for their incredibly small stature, and researchers now suspect that this trait has evolved several times to help these people better adapt to their unusual lifestyle.

Researchers from the Luis Barreiro Lab recently teamed up with several other experts to study the Batwa and Baka people, who, respectively, dwell in the east and west parts of the Central African rainforest.

What makes these groups unique is that they continue to lead a hunter-gatherer way of life, even after other peoples in the region began to take up agriculture. They are also strikingly short, even compared to the other local populations, with their men - the taller of the genders - barely ever passing five feet tall.

For a long time, it remained unclear what exactly caused these pygmy groups to become so short, nor could researchers explain what was keeping them this way.

Some argued that their shortness was a simple consequence of being undernourished from childbirth. The rainforest, while diverse, is not an ideal source of wild edibles for humans. Even the animals man is likely to hunt are difficult to catch in these dense forests. With that in mind, pygmy cultures emphasize the conservation of food and that may have simply limited growth potential.

However, according to a study recently published in the journal Proceedings of the National Academy of Sciences (PNAS), genetics appear to be the true cause.

Researchers gathered genetic data from the Batwa and Baka people and quickly identified striking changes in the part of the human genome that is known to influence human growth hormones. Even more interesting, this mutation appeared to be a different one in both populations, meaning that they independently developed.

Luis Barreiro of the University of Montreal and the senior author of this recent study, told National Geographic that it is very strong evidence that the groups likely found shortness beneficial, naturally selecting the gene through a process called "convergent evolution."

"We have found the strongest evidence yet that the pygmy phenotype is controlled by genetics," he said, adding that the unique phenotype likely helps them need less food and expend less energy while traversing the rainforest.

The Barreiro team plans to continue studying these intriguing populations, given their curiosity about other evolutionary events, such as the development of unique immune responses.

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