http://blogs.discovermagazine.com/gnxp/2011/07/asian-negritos-are-not-one-population/

There seem to be some Mayas who have some Pygmy-like genetics. I can’t say much more but it’s something more than just malnutrition and stress. Height have both environmental and genetic components: Japanese did not grow Nordic-like in size with development and improved nutrition: genetic elements also matter.

http://www.sydneyline.com/Pygmies%20Extinction.htm

This is an article about their rather taller modern descendents.

http://www.theaustralian.com.au/in-depth/aboriginal-australia/the-short-mob-goes-back-a-long-way/story-e6frgd9f-1225987410521

http://www.youtube.com/watch?v=y2IhVpjYUSI#t=58m30s

http://www.newyorker.com/archive/2004/04/05/040405fa_fact?currentPage=5

«In the early nineteen-seventies, when the anthropologist Barry Bogin first visited Guatemala, the country’s two main ethnic groups seemed to live on different social planes. The Ladinos, who claimed primarily Spanish ancestry, were of average height. The Maya Indians were so short that some scholars called them the pygmies of Central America: the men averaged only five feet two, the women four feet eight. The Ladinos and the Maya shared the same small country, so their differences were assumed to be genetic.
But when Bogin, who now teaches at the University of Michigan, began taking measurements he soon found another cause. “There was an undeclared war going on,” he says. The Ladinos, who controlled the government, had systematically forced the Maya into poverty. Whether they lived in the city or in the countryside, the Maya had less food and medicine, and they had much higher rates of disease.

A decade and a half later, after civil war had erupted and up to a million Guatemalans had fled to the United States, Bogin took another series of measurements. This time, his subjects were Mayan refugees, between six and twelve years old, in Florida and Los Angeles. “Lo and behold, they were much taller than the Maya in Guatemala,” Bogin says. By 2000, the American Maya were four inches taller than Guatemalan Maya of the same age, and about as tall as Guatemalan Ladinos. “As far as I know, it’s the biggest increase of its kind ever measured,” Bogin says. “It shows that they weren’t genetically small. They weren’t pygmies. They were suffering.”»

I gave my ideas on the physiology behind the low stature of Pygmies and Negritos in a paper cited here, together with some data on UV light levels in the rainforest:

http://en.wikipedia.org/wiki/Pygmy_peoples

It is important to note that living in a rainforest is a very different proposition if you are an agriculturalist to being a hunter-gatherer. Only the latter actually live under the rainforest canopy and are subjected to low UV levels. Also, it is the combination of living under the canopy as hunters and having dark skin which produces low stature.

Wikipedia seems to think that the Sentinelese are Negritos.

There are some Maya tribes who are Pygmy-sized. I helped to interview some of them years ago for a community radio (they were touring Europe explaining their problems in Guatemala or Mexico can’t recall) and their stature, who nobody had mentioned beforehand, truly surprised me (Pygmy sized, just like that picture above: their heads were below my shoulders like those of rather young children but were fully grown adults). We usually say just “Mayas” but they are a very complex network of tribes and languages, possibly not even mutually intelligible, and I do not know the peculiarities well enough to explain.

I imagine that for some reason this particular tribe (maybe more ancient than others in the jungle?) re-evolved this short stature. Or maybe retained the relevant genetics? Both?