A new study shows that, unlike humans, grey hair in chimpanzees is not an indication of their age.
Researchers from George Washington University have revealed that, for chimps, the relationship between going grey and ageing is not as black and white as you might think.
In most mammals, age can be approximated by considering the proportion of grey hairs that an animal possesses. This is true for humans as well, most of the time anyway. But for our closest ape relatives, it’s not so simple.
Greying is a prominent trait amongst chimpanzees, but at an individual level there are significant variations in pigmentation. It appears that chimps begin going grey up until middle age, at which point the process stagnates.
This was discovered through a simple experiment. Photographs of two subspecies of wild and captive chimps were analysed and rated on the amount of grey hair they each possessed. This was then compared to the ages of each chimp to find a relationship between the two.
The resulting discovery means that attempting to age chimps solely on hair colour is ineffective.
Lead author of the study Elizabeth Tapanes, a PhD candidate in the GW Department of Anthropology, describes this revelation.
“With humans, the pattern is pretty linear, and it’s progressive. You grey more as you age. With chimps that’s really not the pattern we found at all,” Tapanes noted.
“Chimps reach this point where they’re just a little salt and peppery, but they’re never fully grey so you can’t use it as a marker to age them.”
The importance of the research
This research is among the first of its kind to examine pigmentation loss in chimpanzees, or any wild mammals. Senior author on the paper and associate professor of anthropology Dr. Brenda Bradley also noted that most existing research into human hair greying is associated with clinical dermatology and the cosmetic industry.
“There’s a lot of work done on trying to understand physiology and maybe how to override it,” Dr. Bradley says. “But very little work done on an evolutionary framework for why is this something that seems to be so prevalent in humans.”
So why don’t chimps go grey in the same way we do?
The research team has hypothesised a number of possible reasons why chimps haven’t evolved the same hair ageing patterns as we have.
It may be the case that maintaining dark hair pigmentation is critical to regulating body heat. Or perhaps the lack of change in hair colour allows individuals to identify each other more easily.
The next step in this research is to look at patterns of gene expression in individual chimpanzee hairs. This will allow researchers to know whether something is happening at a genetic level to cause the pigmentation patterns we see.
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