The process by which humans began to lose their body hair

Photo by Julia Filirovska on

Humans don’t have it, but other mammals like orangutans, mice, and horses do. For a long time, it has been mysterious to scientists why humans have such a small amount of body hair compared to other mammals. However, the story of how humans and other mammals lost their locks is just beginning to be revealed thanks to a groundbreaking analysis of genetic codes from 62 animals.

University of Utah Health and University of Pittsburgh researchers write in the journal eLife that humans seem to have the genes for a full coat of body hair, but such evolution has blocked them. These findings identify a group of genes and regulatory areas of the genome that are required for hair growth.

Important questions concerning the mechanisms that produce this basic human feature are addressed by the findings. According to the researchers, this could pave the path for novel treatments in balding, chemotherapy-induced hair loss, and other hair loss problems.

This research further demonstrates that this similar method has been used by nature at least nine times before in mammalian species from vastly diverse evolutionary lineages. When they lost their hair and fur, the ancestors of modern rhinos, naked mole rats, dolphins, and other hairless mammals all followed a similar evolutionary route.

Human geneticist at U of U Health Nathan Clark, Ph.D., who conducted much of the research at the University of Pittsburgh with Amanda Kowalczyk, Ph.D., and Maria Chikina, Ph.D., says that they have adopted the unique approach of harnessing biological diversity to learn about human DNA. With this information, they can zero in on certain parts of human genome that play a role in health.

Hairiness takes many forms across the animal kingdom, from the harsh hair of a monkey to the silky fur of a cat. It’s the same with being bald. Although humans have that distinctive crown on the heads, body hair is so fine that we considered “hairless.” Some of these other mammals include the hairless elephant, the hairless pig, and the mustachioed walrus.

A receding hairline can be advantageous in some situations. Elephants benefit from reduced body heat retention in hot areas while walruses benefit from less drag in the water when they don’t have thick coats of hair. Kowalczyk’s research of this and other hairless mammals discovered that they share mutations in many of the same genes, despite the different reasons. Among these are genes for keratin and other components of the hair shaft that are necessary for hair growth.

The research also demonstrated the significance of regulatory areas of the genome. Although they don’t directly code for hair-producing structures, these areas do have an impact on hair production. The timing and location of gene activation, as well as the quantity produced, are controlled by these factors.

In addition, the analysis located genes for which the function in hair growth was unknown. When considered in combination with other evidence, such as skin-based indicators of activity, these results suggest a new collection of genes that may play a role in hair development.

In regard to genetics, the researchers don’t know much about a good number of genes. They hypothesize it play a part in hair development and maintenance.

Clark, Kowalczyk, and Chikina sought to uncover the mystery of mammalian hair loss by looking for genes in hairless animals that had developed at quicker rates than their equivalents in hairy animals.

Clark believes that as animals experience evolutionary pressure to reduce hairiness, the role of the genes responsible for hair loss decreases in significance. This is because they increase the rate of natural selection-permitted genetic alterations. Hair thinning could be caused by alterations in one’s genes.

The researchers used computer approaches that allowed for the simultaneous comparison of hundreds of genomic areas to conduct the search. They examined 19,149 genes and 343,598 regulatory regions that were conserved among various mammalian species. They did this by actively discounting genomic areas that contribute to the evolution of other species-specific features, such as the ability to thrive in aquatic environments.

Clark explains that the success of the strategy was shown by the fact that known hair genes were found through the unbiased screen. In addition, it shows that the less well-defined genes found in the screen may be just as crucial for hair development (or lack thereof).

To define genomic areas implicated in cancer prevention, lifespan extension, and the knowledge of other health issues, Clark and colleagues are currently employing the same approach.

Clark explains that this strategy is useful because it allows researchers to identify the universal genetic pathways that underlie a wide variety of traits.


Kowalczyk, A., Chikina, M., & Clark, N. (2022). Complementary evolution of coding and noncoding sequence underlies mammalian hairlessness. eLife11, e76911.