Research Reveals Human Body Hair Genes Are Still Here

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About a million years ago human beings lost most of their body hair, a key evolutionary moment that involved major changes in the same set of genes that determined whether many of our fellow mammals retained or lost their hair. fur, according to new research.

The study, published in the journal eLife, compared our genetic patterns to those of 62 other mammals, including elephants, manatees and armadillos, examining how hairlessness evolved in different species at different times. The work also identified new genes and gene regulators linked to body hair, a discovery that could one day be used to treat millions of bald Americans.

The technique of comparing vast changes in the genetic codes of different mammals may also allow scientists to investigate questions with profound implications for human health: which genes evolved to protect naked mole rats from cancer, and can they be manipulated in humans to treat or prevent disease? What genetic changes allowed bowhead whales to live up to 200 years, far longer than any human, and can this knowledge be used to increase our lifespan?

“I think it’s a very powerful application,” said Peter Sudmant, assistant professor in the department of integrative biology at the University of California, Berkeley, who was not involved in the study. The research method used came at a time when sequencing technology is rapidly advancing, allowing scientists to read long DNA sequences faster and more accurately.

“I think we’re on the cusp of a very important era of medical genetics and comparative evolutionary genomics,” Sudmant said.

Hundreds of genes were likely to have been involved in losing most of our body hair, said Nathan Clark of the University of Utah, who led the study with Amanda Kowalczyk of Carnegie Mellon University in Pittsburgh and Maria Chikina of the University of Pittsburgh. Using computational tools they helped develop, the authors discovered that although the genes for full body hair coverage remain in our genetic code, they have been muted.

“The initial hair loss in many species was likely very adaptive,” Clark said. “When you think about it, it’s clear that a dolphin swimming in the water, or a whale or a manatee, would be greatly slowed down. They need to be streamlined. They don’t need that hair covering anymore.

In the case of humans, one theory holds that hair loss has proven advantageous for hunting in hot climates. Less hair, coupled with development of a system that allows the body to cool itself through perspiration, may have been key changes that allowed humans to become better hunters, capable of hunting certain prey to exhaustion.

Although the fossil record is insufficient to determine precisely when ancient humans lost all their hair, Clark said: “It probably happened when we left the shady canopy of trees and then supposedly headed to walking through open areas… so heat dissipation probably became a pretty big thing for us, and the ability to sweat probably came along with it.

“That would be my guess,” Clark said, clarifying that, “this document doesn’t prove it.”

What the new study shows is the insight that can be gained by taking a multi-species view of evolution. Trying to pinpoint specific genes that went off in an animal that lost its hair would be, as Clark put it, “a needle in a haystack problem.”

However, finding genetic changes common to many animals that have lost hair is much more manageable. Scientists can align each animal’s genetic blueprints and note areas that have changed rapidly in some species while remaining constant in others. The approach capitalizes on an underestimated evolutionary fact: despite vastly different appearances and behaviors, humans share much of their DNA with other mammals: 99% with chimpanzees, 85% with mice and 80% with cows.

Clark and his colleagues compared more than 19,000 genes and nearly 350,000 regulatory regions and focused on those related to hair maintenance or hair loss. Many genes linked to hair growth contain instructions for making the protein keratin, which forms hair, nails and the outer layer of skin.

Scientists have examined animals that have lost all their hair as well as others, such as bison, guinea pigs, aardvarks and bears, that have retained their fur. They designed their study to ignore genetic regions that code for two confounding variables: living in water and large body size. A disproportionate number of fine-haired mammals are large, and those living on land in hot climates would struggle to dissipate heat.

Of the animals that lost their hair, some may have experienced the evolutionary change much more recently.

“If you look at African elephants and Indian elephants, they’re relatively hairless, but they have very close relatives that lived for hundreds of thousands of years and were completely woolly,” Clark said. “You have this dichotomy where [woolly mammoths] went north and kept all their thick hair, and [elephants] are in the south and they have lost everything. They have very sparse hair coverage.

The process of body hair loss was likely very slow, and in mammals it happened at least nine times, according to the article. The key factor determining the duration of the transition was whether the lack of hair provided an animal with a specific advantage. If so, the selection pressure favored animals whose genes for body hair were reduced or turned off.

For example, a warmer climate that reduced vegetation in the tundra is thought to have contributed to the extinction of woolly mammoths around 10,000 years ago.

“If the woolly ones who couldn’t sweat well died because they got too hot trying to hunt for a food source, then yes, that would be a big disadvantage,” Clark said.

If there was a clear benefit, the hair loss could have happened over hundreds of generations, taking thousands of years, Clark said. If there was no advantage but the hairs just weren’t important anymore, so it probably would have taken thousands of generations or more.

The technique used in the article also sheds light on the least understood areas of our genetic fingerprint. While around 20,000 genes carry the instructions to make proteins, they represent only about 2% of the genome. Other areas work much like a dimmer on a light, affecting the degree to which genes or groups of genes are turned on or off. Turning on a gene almost always results in the production of more of a specific protein.

“Not as much work has been done on these regions,” said Mark Springer, professor emeritus of evolution, ecology and organismal biology at the University of California, Riverside. This article “really points the way forward for future research. There is much more to learn.

In 2017, Clark and some of his colleagues used a similar technique to compare the genomic evolution of animals that live above ground with blind mammals that live below ground. They discovered many genes related to vision and skin that changed faster in animals living underground. They also identified genes and regulatory regions that could be used as potential targets for the treatment of congenital eye diseases.

“I have to say, this stuff is incredibly cool,” Sudmant said. “We are looking at 75 million years of evolution. The fact that you can look at the molecular pathways that influence a trait like body hair is mind-blowing.

Research Reveals Human Body Hair Genes Are Still Here

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