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A photo of Batwa women

Members of the Batwa people, like these from the Bwindi Impenetrable Forest in Uganda, have an average adult height several inches shorter than that of nearby tribes.

Photograph by Andrew Aitchison, In Pictures/Corbis

Carrie Arnold

for National Geographic

Published August 18, 2014

It's not another tall tale: Evolutionary biologists have developed a new understanding of the genetic basis of short stature in humans. Also known as the pygmy phenotype, a study published Monday in the Proceedings of the National Academy of Sciences shows that this trait has evolved several times over the course of human history.

In the Central African rain forest, several groups of hunter-gatherers are significantly shorter than their agricultural neighbors are. Both the Batwa people in the east and the Baka in the west are commonly referred to as pygmies.

But exactly what factors were contributing to their reduced height wasn't clear. By analyzing the genomes of the Batwa and the Baka, and comparing them with the genomes of their average-height neighbors, the researchers were able to show that these two groups of humans showed variations in the region of the genome that codes for human growth hormone receptors and bone formation.

"We have found the strongest evidence yet that the pygmy phenotype is controlled by genetics," said Luis Barreiro of the University of Montreal and the senior author of this recent study.

Although height is a tremendously variable trait among humans, several rain forest-dwelling populations in Asia and Africa have been noted for their unusually short stature. The average height among Batwa men (60.1 inches, 152.9 centimeters) and women (57.4 inches, 145.7 centimeters) is significantly lower than in neighboring Bakiga men (65.1 inches, 165.4 centimeters) and women (61.0 inches, 155.1 centimeters).

Biologists soon began to wonder why height was so different in these populations.

Some scientists hypothesized that environmental factors were the main cause. Rain forests might be biodiverse, but it's extraordinarily hard for humans to find food there. People like the Batwa may be short simply because they are not receiving proper nourishment to grow to their full height.

Other scientists, including Barreiro, thought that gene variations might be contributing to the pygmy phenotype. For one, it could be easier for shorter individuals to keep their bodies from overheating in the tropical humidity. Some of Barreiro's own work revealed that traveling through the rain forest involves a lot of ducking under things, which requires a lot of energy. Shorter people don't have to duck as much and consequently burn fewer calories as they walk through the rain forest.

Significant Genetic Differences

Barreiro and colleagues gathered genetic data from the Batwa and Baka peoples, as well as from three neighboring agricultural groups of average height. When they scanned different regions of the genome, they found significant genetic differences among the Batwa and Baka in an area of the genome that is known to code for the receptors for human growth hormones.

When the researchers looked more closely, they found that these genetic differences weren't just random chance and that the first Batwa and Baka people just happened to be short. Instead, these genetic differences were somehow benefiting the individuals living in these rain forest environments. It's an example of convergent evolution, Barreiro says, in that the same trait (short stature) evolved independently in several different populations.

When they looked at when these mutations might have happened, Barreiro and colleagues found that they were relatively recent events, having occurred separately in both the Batwa and the Baka. This showed that whatever factors were selecting for short stature were fairly strong and could exert their effects relatively quickly.

"This study is one of the most significant advances made on the genetic determination of the pygmy phenotype so far," said Paul Verdu, an anthropologist and ethnobiologist at France's National Museum of Natural History.

The results will help provide an understanding not just of the pygmy phenotype, but also of the evolution of the tremendous amount of diversity in our species.

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6 comments
Franklin Ampy
Franklin Ampy

This is not surprising since almost everything (even diseases) concerned with living organisms appear to have some kind of genetic or epigenetic basis.

James Kohl
James Kohl

Excerpt 1) : People like the Batwa may be short simply because they are not receiving proper nourishment to grow to their full height.

Excerpt 2) : Shorter people don't have to duck as much and consequently burn fewer calories as they walk through the rain forest.

This could be referred to as the "duck-centric" theory of human evolution and be compared to the snake-centric theory of human brain evolution (see: http://news.sciencemag.org/evolution/2013/10/did-snakes-help-build-primate-brain).

Indeed, the theories might be combined in an effort to teach serious scientists why Dobzhansky implied that looking at morphological phenotypes without understanding the molecular mechanisms of biologically-based cause and effect was like "bird watching" or "butterfly collecting."  In 1964, he said: "Bird watching and butterfly collecting are occupations manifestly unworthy of serious scientists!"
http://icb.oxfordjournals.org/content/4/4/443.citation

Of course, he was right!

Excerpt 3); It's not another tall tale: Evolutionary biologists have developed a new understanding of the genetic basis of short stature in humans.

Of course, it is another tall tale; it even parallels the one about the dinosaurs shrinking across millions of years to become modern populations of birds. However, this nutrient-dependent human "evolution" seems to actually take us from that pseudoscientific nonsense to what is known about biophysical constraints on the nutrient-dependent pheromone-controlled physiology of reproduction, which links ecological variation to ecological adaptations via conserved molecular mechanisms in species from microbes to man.

Simply put, either these modern human populations "evolved" very quickly in the context of the "duck-centric" and "snake-centric" theories, or they ecologically-adapted as did all populations of all individuals with all cell types that are differentiated by the epigenetic effects of food odors and pheromones on their nutrient-dependent pheromone-controlled physiology of reproduction.

See for examples: http://www.ncbi.nlm.nih.gov/pubmed/24693353

anne boad
anne boad

Yet many folk still deny the possibility of evolutionary selection. It must be hard for them.


James Kohl
James Kohl

Serious scientists may not be willing to continue to sit by while theorists invent more theories. For example:"Our principle aim in the lab is to attack scientific dogmas. Mainly, we aim to use powerful genetic tools to discover novel biological principles by which RNA affects formation and inheritance of complex traits." http://www.odedrechavilab.com/About.aspx

This does not imply that they intend to be polite. However, the only way to attack dogma is to provide experimental evidence of biologically-based cause and effect to refute theories. 

Some attacks on dogma will obviously be based on experimental evidence of nutrient-dependent pheromone-controlled ecological speciation, since it would be impossible for theorists to mount a counter-attack that included any evidence that any individual of any species does not need to eat to reproduce.


See: Starvation-Induced Transgenerational Inheritance of Small RNAs in C. elegans http://www.cell.com/cell/abstract/S0092-8674(14)00806-X


Oddly, evolutionary theorists have continued to place Darwin's nutrient-dependent 'conditions of life' in a secondary position compared to mutation-initiated natural selection or whatever else they think led to the evolution of biodiversity. They should probably prepare to defend themselves from ridicule by serious scientists as others begin to take Dobzhansky (1964) seriously.


"Bird watching and butterfly collecting are occupations manifestly unworthy of serious scientists!"
http://icb.oxfordjournals.org/content/4/4/443.citation

reva madison
reva madison

@anne boad No, the problem is that they dont THINK about it at all.  It is a mute point with them, because it could not happen.  On the other hand, I, for one, was not born with the inbred idea to stick my head in the sand when any scientist says something I wasnt brought up to believe.

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