Feel Short? Blame Your Ancestors

The researchers determined that across all hunter-gatherer groups, body size directly relates to population density. The bigger the population, especially within island or island-like communities, the smaller the people will be. One example of an island-like community would be a tropical rainforest group that is clustered in a central spot. Such people tend to be shorter than groups living in tundra, savanna, desert and other open habitat areas.

Since prior research found that nutrition over time affects human height, the scientists theorize that in more densely populated areas, there is greater competition for resources and a higher instance of disease spread. Since mortality is consequently higher, natural selection favors earlier maturation so that individuals can reproduce before they die.

"For any given growth rate, if you stop growing earlier and start reproducing earlier, you are a smaller adult," Walker said. "This may be going on in some human groups where mortality is high."

Francis Collins, director of the National Human Genome Research Institute, agrees that a variety of factors, including genetics, prenatal environment and diet, interact to determine how tall someone grows. Collins and his colleagues even recently linked a gene connected with arthritis development to human height.

"Many of the genetic variants involved in height likely will have only small effects, so it's going to take a lot of work involving very large sample sets to uncover all of them," Collins said.

Walker and Hamilton, however, think that other scientists may be overlooking the effects of ancestral population density and ecology on height, which may resolve longstanding anthropological mysteries. For example, they believe that the new, hotly debated "hobbit human," Homo floresiensis, evolved to become so small (just over 3 feet in height) because it was in a closed island society.

Neanderthals, on the other hand, tended to be tall and stocky, possible indicators that they lived in less densely populated areas.

Related Links:

Jennifer Viegas' blog: Born Animal

National Human Genome Research Institute

Societies Ranked by Height

Max Planck Institute for Evolutionary Anthropology