Posted on 02/04/2025 9:58:23 PM PST by Red Badger
Humans are the only mammals with long hair on their heads. Scientists look into what drives this unique feature.
Humans evolved long hair on their head to prevent overheating and excess water loss when walking under the hot sun in Africa.
iStock, Delmaine Donson
In 2004, a Chinese woman named Xie Qiuping won the Guinness World Record for the longest human scalp hair at 5.627 meters—the length of an adult male giraffe! While this is an anomaly, humans are the only mammals that have negligible body hair, but extremely long hair on their heads. “It's such an important part of our identity as a species and yet, we understand so little about it,” said Maksim Plikus, a developmental biologist at University of California, Irvine, who studies the regeneration of hair.
Now, in a paper published today in the British Journal of Dermatology, Plikus and his colleagues—Nina Jablonski, an anthropologist at The Pennsylvania State University and Sung-Jan Lin, a dermatologist at the National Taiwan University—discuss why and how humans evolved this unique feature and speculate on the possible genetic mechanisms that drive the exuberant growth of these long and luscious locks.1
One theory dates back to life millions of years ago, when human ancestors roamed across Africa, exposed to the blazing sun. As they spent a lot of time outdoors searching for food and water, they needed efficient mechanisms to keep their body cool. “In human evolution access to fresh water was always something that individuals and groups had to think about and plan over,” Jablonski said. “So having a thermoregulatory mechanism that would help to conserve precious water would be advantageous.” The absence of fur and abundance of sweat glands helped keep the body cool even after bouts of exercise, such as hunting animals.2 However, the head received the most solar radiation and probably needed other ways to keep it from overheating. Prehistoric cave paintings from Europe and Australia and Egyptian mummies with preserved hair suggest that long hair was a universal feature across different populations of humans.3,4
Tightly curled and long scalp hair of ancient hominins could have evolved to shield the scalp from the sun, reduce heat transmission due to the air pockets between the curls and minimize water loss through sweat.5 While it is not known when curly hair emerged, it is likely that long hair growth evolved later to compensate for curly hair’s tendency for wear and tear.
Hair length depends on the hair growth cycle. A hair follicle can either be in the active growth phase called anagen or the rest phase called catagen.6 Stimulatory signals trigger the proliferation of matrix cells in the hair follicle during anagen, lengthening the hair strand. A continuous supply of these cells is essential for the sustained growth of hair. A typical human scalp hair follicle stays in anagen for five to seven years, producing hair that is 50–110 centimeters (19–43 inches) long. For exceptionally long hair, such as that of Qiuping, the matrix cells would have to undergo over 11,000 divisions over more than 30 years!
“Hair follicle is like a biological 3D printer. Based on the molecular program you feed it, it'll print something tiny or something super long,” said Plikus. “You don't need to add any new components. You just have to instruct the various cells to work for longer and print for longer.”
Though no other mammal can boast of the exceptional hair lengths seen on human heads, the potential for long hair growth is conserved across the class, from the wispy “mustaches" of emperor tamarin monkeys to the meter-long body hair skirt of extinct Woolly mammoths. Studies on human dermatological conditions that alter hair length could provide insights on the molecular basis and genetic regulators of long scalp hair in humans. Mutations in fibroblast growth factor 5 (FGF5), a protein that promotes catagen entry, cause familial trichomegaly, a condition where body hair and eyelashes grow unnaturally long.7 Since the mutations prolong anagen throughout the body, it is likely that the gene is differentially controlled through modifications in its regulators in the scalp cells. Contrastingly, variants of the protein Wnt Family Member 10A shorten anagen, possibly causing conditions like androgenetic alopecia, or male pattern baldness.8
Scientists have started to dig deeper in the enigma of human scalp hair. Comparative studies of body and head hair using RNA sequencing and next-generation spatial sequencing, transplantation of human hair to rodent models, constructing computational models of hair growth and examining the intricacies of hair growth in individuals could unravel the molecular drivers of human hair growth. A clearer picture of how human scalp hair reaches considerable lengths could then lead to new therapeutic leads for conditions like hair loss or genetically stunted hair. “How could you treat a disease of short hair if you didn't even know what's the normal recipe for long hair?” Plikus pointed out.
Bovine Beatles..................
If humans evolved long hair as sun protection then why do so many adult men NOT have long hair? Do they not need sun protection?
Read “The Descent of Woman” by Elaine Morgan. Such a drastic mutation as continuously growing head hair in adult females is, by necessity, connected to procreation and child rearing.
Humans have the longest comparative child rearing lifespan of all animals. It requires drastic measures. Mothers and babies are key. Humans evolved in a marine environment during a critical period when land predators ran mothers and their infants into the surf. Mothers with upright gaits and long hair, along with swimming babies with strong hand grips, became requirements of human survival.
Fathers were unimportant.
“Humans evolved ...”
Nope.
Agreed. The only mammal? How about an easier answer...cause we're humans created by God.
Another View is that men, being the ‘protectors’, and needing to fight off other men from other tribal groups, long hair was a disadvantage and a problem.
Women then, being the procreators, would choose to mate with the men who were more victorious in the fights, in so doing they would pass along the male pattern baldness gene...........
horses don’t have manes? male lions don’t have manes?
Yes, they are manes, not head hair..................
Then why would women require long head hair?
I get the wolf man beard up my cheeks.
I just go to a proper old fashioned barber with a straight razor in the regular. It’s really the only solution. You need a second person to look at you to get your face balanced.
Because only humans charge such outrageous prices for haircuts!
Men, OTOH, find women with long tresses to be more attractive, especially red ones..............
“The absence of fur and abundance of sweat glands helped keep the body cool even after bouts of exercise, such as hunting animals.”
Not sure this will go over well with the ‘Vegan crowd’.
.....to this:
Conversely, human ancestors of another line went from this:
.....to this:
How and why did one line evolve so much faster?
God only knows!...................
Joe Biden knows a lot about leg hair.
That nose hair seems to have activated for some reason.
Hair follicle is like a biological 3D printer. Based on the molecular program you feed it, it’ll print something tiny or something super long.
If so why do I keep finding mine in the shower on my pillow in the sink I feed it and noting happens.
They are trying to escape!.....................
Maybe I believe they reverse direction my eyebrows getting longer now nose and ear hair needless to say in other places.
For the combover.
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