Jun 17, 2021 —
Photo: public domain
Animals in the wild do not need haircuts; why do humans? And why just on the head? Our scanty (by comparison) body hair grows only for a couple of months, then stops. Head hair will grow throughout its life of several years, and doesn't stop until it falls out.
Martha Foley and Curt Stager have a longhair discussion.
Martha Foley: I have to get a haircut this afternoon, I have to get a haircut every month. Why? Why do I have to get a haircut? I mean, because it keeps growing. Maybe the question should be "why does the hair on our heads just keep growing and growing and growing? Why doesn't it stop?"
Curt Stager: I don't know.
MF: Like... my dog doesn't have to get a haircut every month.
CS: It's neat. Some of the things right before your eyes in daily life you think are so well known that all the answers would be known to science. And here's one that's a standing mystery.
MF: I don't think the hair design and hair care industry has anything to do with it...
CS: Well, they pretty much don't care the "why" they just deal with the reality that if you talk to other experts who try to answer this, they may even say with great authority "it's because of this or because of that." But they all say it with equal authority. And they're saying different things. The fact is, it's a mystery.
MF: Nobody knows.
CS: Nobody really knows and to think about it, kind of exposes the mystery. It really is interesting because we have hair on our arms and our legs and you don't have to... You know, if you let it alone, it comes to a certain length, then it stops. And it's shorter. And so like as a biologist, oftentimes we say "oh, we're related to other animals, but we're different from the other primates because we're so hairless, you know." But actually the abundance of hairs, like on my arm, supposedly the number of hairs in a certain area is the same as a furry mammal. It's just that they're not long and heavy. It's kind of like the under-fur, the fine stuff. So the numbers of hairs is not all that different. It's just how thick it looks.
MF: Well, and also, I mean, back to the hair on the head. I mean, what is it about that? Are there other animals? Let's think, that have to get a haircut?
CS: Yeah, do bears have to shave?
MF: It's not just grooming. I mean, it just stops.
CS: Right. Well, there are different ideas. You think, well maybe it's because it's eroding. You know, maybe, and we have to now imagine humans in the distant past because the way we live now...
MF: You mean it's just wearing off.
CS: Yeah. So maybe try to think back in the cave person days or the early you know...
MF: I don't remember back that far.
CS: That's the biggest problem because actually we don't know how hairy our ancestors were because that stuff isn't preserved. We have the bones and we don't have the hair.
MF: We just have the drawings from our imagination.
CS: They didn't take pictures with their iPhones and post them somewhere. So you don't know what they looked like. But you think, okay, well maybe it's because it erodes. And actually that's true for say, birds, they have feathers but it's the same material that hair is made of and their feathers erode.
MF: They wear out.
CS: They wear out. And you know bird specialists that catch migratory warblers, let's say, they can say oh, this one has come a long way from its other place and look at the tips of the feathers, they're all wearing off and birds have to replace their feathers by molting, you know, every year or....
MF: But those feathers don't keep on growing. I mean, they just have to replace the whole thing. Well our hair I mean, it doesn't last forever. What does grow for us, a particular hair grows for a number of years, falls out, and then gets replaced.
CS: Yeah, and the different kinds of hair have different, you could say, life-spans. Although it's not like a living substance, the root has living cells in it that make the hair get longer and the hairs on your head last several years before they stop growing. And they'll fall out one by one, you lose like maybe 100 a day all the time in the different stages. The ones, let's say on your arm, they only grow for about a month and they stop. So it's even like a different ecology of hair in the different habitats of your body.
MF: So they're reasonable, those hairs on your arm, they know when to stop.
CS: So it's hard to think of...is our head hair growing because we were doing something with our heads that would erode it? It's hard to imagine what would erode that off that wouldn't be eroding off your hands or your arms, you know? So that one probably doesn't make sense.
MF: Now sheep, we shear sheep. We harvest hair or fur, is this the same thing, hair and fur?
CS: Right. There's not even a clear definition of what that difference is. But yeah, you think of llamas or sheep or goats and you...
MF: Well some you pluck in some you shear.
CS: And it gets pretty long if you don't do it, but then you think, well those are domestic animals. So it's the same thing. Maybe that's just doing it because of something we've done. If you think of things that live out in the wild, there's pretty much... everything just kind of grows to a certain length and stops.
MF: Okay, that's starting to make sense, but as we say, when we don't know the end of the story...time will tell. Thanks very much Dr. Curt Stager at Paul Smith's College. I'm Martha Foley at St. Lawrence University.
Natural Selections is a weekly conversation about the natural world aring Thursday mornings on NCPR. North Country Public Radio is listener (and reader) supported. You can help us provide more content like this here. And thanks!
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