For chimpanzees, gray hair isn’t necessarily a sign of old age

WASHINGTON — Finding that first gray hair is a rite of passage for humans. It’s also a sign, of course, that we’re getting older — and more are on the way. For chimpanzees, however, hair color doesn’t follow the same linear path. As scientists from The George Washington University explain, observing gray or silver hair on a chimpanzee doesn’t mean you’re looking at an old timer.

While these findings may sound fairly inconsequential at first, in actuality they challenge the significance of the gray phenotype among non-human beings. Patches and areas of gray hair are very common in chimpanzees. The amount and locations of discoloration, however, varies greatly from chimp to chimp.

Most chimpanzees see portions of their hair gray over time until they reach middle age. After that point the graying process appears to level off.

“With humans, the pattern is pretty linear, and it’s progressive. You gray more as you age. With chimps that’s really not the pattern we found at all,” explains lead study author  Elizabeth Tapanes, a Ph.D. candidate in the GW Department of Anthropology, in a release. “Chimps reach this point where they’re just a little salt and peppery, but they’re never fully gray so you can’t use it as a marker to age them.”

Gray matters for chimps

To produce evidence that gray hair is not indicative of old age among chimps, the study’s authors gathered together a series of photographs of two chimpanzee subspecies. Sets of photos for both subspecies included wild and captive chimps.

Researchers closely examined each photo, and took note of the chimps’ gray hair. They then cross examined each chimp’s recorded age with the amount of visible gray hair on their body.

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As far as why chimp hair doesn’t lose its color in the same way as human hair, the research team says there are a number of possible explanations. One theory is that chimpanzees need to retain their dark pigmentation (at least on most of their body) for the entirety of their lives in order to identify one another or perhaps thermoregulate.

New research on old theory

The idea behind this research came to lead author Dr. Brenda Bradley, an associate professor of anthropology, as she was observing chimpanzees in Uganda for five years. At the time, she kept assuming the chimps with more gray hair were older. After learning that wasn’t the case, she set out to explore the topic further.

Surprisingly, there hasn’t been much research performed on gray hair development in chimpanzees, or any other wild animal for that matter, before this project. Of course, most of the research on graying hair among humans focuses on the cosmetic side of things.

“There’s a lot of work done on trying to understand physiology and maybe how to override it,” Dr. Bradley notes. “But very little work done on an evolutionary framework for why is this something that seems to be so prevalent in humans.”

Moving forward, Dr. Bradley and her team want to continue their work by examining gene expression patterns in singular chimpanzee hairs.

The study is published in PLOS ONE.

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