Hair is an important feature of primate diversity and evolution—including among humans. It serves functions that are tied to thermoregulation, protection, camouflage and signaling.
But the evolution of wild primate hair has remained relatively understudied—until recently.
Researchers from the George Washington University Columbian College of Arts & Sciences' Center for the Advanced Study of Human Paleobiology (CASHP) examined the factors driving hair variation in a wild population of lemurs known as Indriidae. They focused on the impacts of climate, body size and color vision on hair evolution. Their findings, published in the American Journal of Biological Anthropology, include:
- Sifaka lemurs, which are native to Madagascar, have denser hair in dry, open environments. The researchers believe that, like early humans, the lemurs’ hair helps protect against the strong rays of the sun.
- Lemurs in colder regions are more likely to have dark hair. This is the first evidence in mammals for a classic pattern in nature called Bogert’s Rule, which states that dark colors could aid with thermoregulation as they help absorb heat from the sun’s rays.
- Red hair in lemurs is associated with enhanced color vision. According to the researchers, populations that can see a larger range of colors are more likely to have patches of red hair.
- Multiple evolutionary pressures may act on one trait and the strength of their influence may vary between species.
“Human hair evolution remains a mystery, largely because hair does not fossilize,” said Elizabeth Tapanes, M.Phil. ’20, Ph.D. ’21, lead author on the paper and now a postdoctoral scholar at the University of San Diego, California. (Tapanes conducted the hair evolution research while a doctoral student at GW.) “The lemurs we studied exhibit an upright posture like humans and live in a variety of ecosystems like early humans, so our results provide a unique window into human hair evolution.”
Associate Professor of Anthropology Brenda Bradley, director of the CASHP Primate Genomics Lab and a co-author on the study, explained that our understanding of hair evolution and diversity in other primates helps us fill in the gaps of the human evolutionary story.
“Most people are intrigued by the diversity of hair on their own bodies, and the variety of hair types among people around the world,” Bradley said. “Understanding hair patterns in non-human primates, such as these lemurs, may provide a comparative context for understanding how variation arose in human hair.”
The researchers noted that follow-up work should focus on samples across smaller geographic or phylogenetic (family-level, genus-level) scales and from diverse non-human and human populations.