The Genetic Story Behind Humans Losing Their Body Hair

New research from the University of Utah Health and the University of Pittsburgh has compared the genomes of 62 mammals, revealing new insights into how humans lost their body hair. The research was published in eLife.

Hairy or hairless?

Our sparse covering of hair puts humans into the “hairless” class of mammals, along with animals including naked mole rats, walruses, dolphins and elephants, worlds away from “hairy” orangutans, horses and mice.

The new study has provided the first insights into how humans and other mammals evolved to be hairless from a genetic perspective. Led by Dr. Nathan Clark, a human geneticist from the University of Utah, the team reveal that humans carry the genes for a full body covering of hair, but they have been deactivated over time.

By screening 19,149 genes and 343,598 regulatory regions with a computational tool called RERconverge, which identifies genes and regions that evolve at different rates, the researchers could compare the genomes of 62 different hairy and hairless mammal species and pinpoint genes important for hair loss.

“As animals are under evolutionary pressure to lose hair, the genes encoding hair become less important,” Clark said. “That’s why they speed up the rate of genetic changes that are permitted by natural selection. Some genetic changes might be responsible for loss of hair. Others could be collateral damage after hair stops growing.”

Genes and regulatory regions are both important

Notably, mutations accumulated in the genes encoding keratin and other elements crucial for building the hair shaft and facilitating growth, and in regulatory regions responsible for guiding when and where hair grows. The screen with RERconverge, combined with additional information about gene activity, also identified new genes involved in hair growth.

The identification of novel genes and regulatory elements suggests these less-well defined regions may be just as important as the well-known hair-related genes for hair growth and maintenance.

This mechanism of hair loss isn’t exclusive to humans, the researchers found. Ancestors of other hairless mammals including naked mole rats, elephants and dolphins followed the same evolutionary path to hairlessness, in at least nine different cases.

By defining the genetic pathways that shape humans’ hairlessness, the study authors hope to provide new insights that can lead to treatments for balding, hair loss after chemotherapy and other disorders that cause hair loss.

Clark and colleagues are now employing the same computational approach to identify genetic regions involved in other health conditions, including cancer.

 

Reference: Kowalczyk A, Chikina M, Clark N. Complementary evolution of coding and noncoding sequence underlies mammalian hairlessness. eLife. 2022;11:e76911. doi: 10.7554/eLife.76911.

This article is a rework of a press release from the University of Utah. Material has been edited for length and content.