Scientists Discover Pygmy Phenotype Evolved Many Times in Humans as Rainforest Adaptation

The small body size associated with the pygmy phenotype seems like it would be a relatively unique trait as a selective adaptation for rainforest hunter-gatherers. Now, though, researchers have found that not all African pygmy phenotypes have the same genetic underpinning, hinting that this is a more recent adaptation than previously thought.

The pygmy phenotype exists in many parts of Africa, Southeast Asia, the Philippines and South America. This phenotype, though, is usually associated with rainforest hunter-gatherer groups who don't farm.

"I'm interested in how rainforest hunter-gatherers have adapted to their very challenging environments," said George Perry, one of the researchers, in a news release. "Tropical rainforests are difficult for humans to live in. It is extremely hot and humid with limited food, especially when fruit is not in season."

In order to learn a bit more about this phenotype, the scientists examined the genetics of the Batwa rainforest hunter-gatherers of Uganda. They then compared their genetics to their farming neighbors, the Bakiga. In addition, the researchers looked at the Baka rainforest hunter-gatherers and their farming neighbors, the Nzebi/Nzime in central Africa.

The pygmy phenotype causes Batwa men to be an average of five feet tall. In women, it causes them to be an average of four foot eight inches. This short stature is not caused by dwarfism, but is the result of a variety of genetic changes throughout the genome that influence height. In all, the scientists investigated 16 different genetic locations that were associated with short stature.

In the end, the researchers found that there was a statistical difference between the two groups, indicative of multi gene adaptation. Interestingly, though, they found that the Baka did not have the same types of changes in the 16 genetic locations.

"What we think we see is that regions of the genome that are involved in the Batwa's Pygmy phenotype do not look the same in West Africa," said Perry. "If the Pygmy phenotype were really old, then we would have expected the locations to be similar."

The findings hint that both of these Pygmy phenotypes arose independently with different underlying genetics. This, in turn, shows that the phenotype evolved at different types and also leaves the door open for a much later development of the Pygmy phenotype adaptation."

The findings are published in the journal Proceedings of the National Academy of Sciences.