Pygmies of western Africa are short—really short. On average, Pygmy men stand just 4’11” tall. Yet their neighbors, a group known as the Bantus, are of average height.

An expert in human genetics with extensive experience working with African populations, Sarah Tishkoff, a Penn Integrates Knowledge Professor, has been conducting research to determine the reason for the height disparity among Pygmies and Bantus.

“I’m really interested in not just stature but in the physiology and the biological adaptation of these populations to their environment,” she says.

Previous studies have suggested that the diminutive stature of the Pygmies may have made them well equipped for the hot climate of the tropical forest, or better able to survive in conditions where food was not abundant. Other scientists proposed that the small size of the Pygmies enabled them to reach sexual maturity at an early age, an important trait for survival given that the average life span of Pygmies is only around 20 years.

Tishkoff worked with colleagues to take genetic samples from 132 individuals in three Bantu populations and three Pygmy populations in Cameroon. Scanning the genomes of the study participants, researchers identified genetic markers that were either characteristic of Pygmies or Bantus. Writing in the journal PLoS Genetics, they reported that the more Bantu ancestry a Pygmy had, the taller he or she was.

When Tishkoff’s team looked more specifically for genes with a role in height regulation, they identified a handful of promising candidates in what she calls a “hot spot” of chromosome 3. These genes appear to do more than control height; they may also play a role in crucial biological functions, such as fortifying the immune system to protect Pygmies from infectious diseases, which are rife in the tropical areas they call home.

“The intriguing possibility this raises is: Could natural selection for short stature have nothing to do with short stature itself?” Tishkoff asks. “Something we propose in the paper is that maybe there was coevolution of a number of genes.” If true, the fact that Pygmies are small may simply be an accidental byproduct of evolution, whisked along through the generations by selection for hearty immune systems or other valuable traits.

Such possibilities give Tishkoff endless inspiration for future study.

“What causes a Pygmy to be short may be very different from what causes a European to be short,” she says, “so we can learn something new from looking at ethnically diverse populations.”