So I was thinking about stuff the other day, as I usually do, when a puzzle presented itself. I pulled out a few hairs on my leg - because that's what I do when I'm thinking - and I wondered how long it would take those hairs to grow back. Then I thought the whole thing through a little more and a question arose.
When someone shaves their legs, how does the hair know it's been shaved so that it can grow again?
If you're wondering how the hair knows when to stop growing you could always cop out and say 'genetics' and you'd probably be right. The hair on your legs is different from the hair on your head, and it only grows so long. But that still doesn't answer the first question, how does the hair know it's been shaved in the first place?
If you think about pulling the hair out that's different, there's nothing where there used to be something, so that's simple enough for the follicle to figure out. But if you just cut it off at the skin, how does the follicle realize the hair isn't as long as your genes say it should be? Something's gotta tell it, right? And then something has to tell it to start growing again.
Ask your doctor that one, I'll bet he doesn't know. You could also ask him why the human body still has an appendix, when keeping a vestigial organ that can get inflamed and burst and kill us seems like a negative evolutionary adaptation. Or ask him how Himalayan monks can raise their body temperature voluntarily to dry out soaking wet sheets that they've been wrapped in.
It's like a big game of Jeopardy without Alex Trebek, but nobody gets to know the answers.
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It could be the solicitation of the hair strands to their follicles due to their weight/mass. The longer the hair, the more its mass and the more any single movement stimulates the follicle in a different way depending on its length so the body realizes how long it is and how much of it has been cut. More so independently from the gravity, something with more mass have more inertia, hence more pull and tug to the hair follicle. In any situation we have some minimal movement so that the body knows how long are our body and head hair, maybe it doesn't need to really "see" the hair panoramic. Think about how much force is needed to stop a truck and how much is needed to stop a motorcycle at the same speed, the truck always "wins", so once a hair exceeds the inertia for which a follicle is programmed to deal with, the body sends a hormonal signal to stop hair production and trigger its, rest, the opposite happens if the hair is cut, the follicle realizes it has less mass applied to the "bed". It's also a myth that hair grows back thicker when shaved, it just has its blunt end.
ReplyDeleteObviously all hair, besides a part of the head hair (not even all of them) of some people, is eventually shed off, but obviously they are programmed to live much more that the time needed to reach their length. At least a few times their length, as you see them all growing back when you shave them.