h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Are humans the only species that suffer male pattern baldness?

Are humans the only species whose hair length doesn't self regulate?

Sheep grow their fleece without break, as do some dog breeds. You have to trim/shear them to prevent overheating, I suppose. It's probably from selective breeding though, because it doesn't seem right...
Would be kind of fun to see a balding old critter though, I don't think there are any

I have to trim my horse's tail regularly or he starts stepping on it...

Human's hair length does self regulate.

If you don't cut it, each hair on your body will continue to grow until it reaches its natural length, will stay at this length for a while and then fall out. Since there are always new hairs growing, the hair length remains constant.

The natural length on somewhere like your arm is about 1cm.

It may look as if the hair on your head just keeps growing forever, but head hair has its own natural length, which is typically about 40cm to 90cm depending on the person. If you let your head hair grow, it will eventually after a few years reach its natural length and will not grow any longer.

There are stories of people growing head hair long enough to touch the ground, but this is very rare. Even these people will have a natural hair length, although it could be very long.

So, Rapunzel may not have been a real person?

I've been trying to grow out my fringe for half a year, and it currently reaches my eyebrows, just as it did in September.

Of course, when it's wet, it's now down past my nose. Mine self-regulates by growing in circles!

Hair.

I've always had a lot of it wherever it grew.

In recent years, my hair line has receded a bit, but at least I don't have a bald spot in the center of my head. At 67, I feel that having any hair at all is pretty good.

I've yet to work out how its possible for my hair to have changed as it has... I always thought the curl or not of hair was determined by the shape of the hair folicle.... which one assumes is a fixed constant, and simularly, I assme the number of hair folicles is a fixed thing too.... yet, since chemo, I've more hair folicles on my head, and some of the hair is slightly wavy very strange... (and this is having gone past the stage of the baby hair appearing, again, then falling out)
Arm hair is curious.

boy does your skin feel so gorgeous without hair on your arms, or indeed without hair anywhere on the body; believe it or not you've probably got very fine hair on your forehead just very very very short and fine; it does feel so much smoother skin without it mind

simularly. having five centimeter long arm hair is just horrid (luckily that was some kind of baby hair too and seems to have vanishd now). hair is just weird

They say that all the cells in your body change over the course of seven years.

I had an uncle whose hair would straight for seven years, and then curly for seven years....

Still kinda weird, as I guess the shape of the hair folicle, made up of probably several thousand cells, must be genetically determined, hence how hair has its genetic basis... Dunno if my hair will stay like this now, or revert back or what pity kinda like it being quite so differnt to how it ever was before

I knew a Rastafarian who hadn't had a haircut in 25 years - it came to about 8" above his waist. When people heard this, they invariably asked "how come you aren't tripping over it?"

His exasperated (but perfectly reasonable) response was usually "You've never cut your eyelashes in your life, have you? So how come you're not tripping over them?"

Bose the same principal apply to circumcision?

Wellll...now that you mention it, I don't think I've ever walked on my foreskin!

(But I bet you 2legs has walked on his. Or at the very least, got somebody else to do it. )

MMM. err. yes. hair is an odd one though, as differnt hairs in differnt parts of the body, are differnt... and I'm trying to recall.... guess its a slightly differnt protein structure in differnt hairs, - head hair, VS arm/leg hair, Vs pubic hair, Vs say eye lashes or eye browse... - cells making them probably differnt; I didn't lose all my head hair, I did* lose all my body hair, but, didn't lose my eye browse, eye lashes, or err, some other hair the growing back of said hair, after its chemically induced 'reset' was very uneven too; head hair started growing as it was still falling out, and my armpit hair still hasn't started regrowing on one side, but just has some very 'soft' looking tentative steps into regrowht on the other pit, oo, about 9 months after the chemical induction of its loss, ended and, for an as yet utterly un-explained reason, my hair line, 'behind' my ears, now almost touches where one's ears issue forth from th e head... which is... just really rreaky!

Before chemical induction of loss, I'd not had my hair cut really since I was in my early teens (about 13 or 14 I think), and it only ever made it to my waist....

Back to patturn baldness, though;

I guess its like ertain animals that have patturning on their skin/fur; I guess its down to gene activation, or, as in case of hair loss, maybe deactivation.... or... not... of course... damnit, gona have to go find out now

Hair today, gone tomorrow.

I'm guessing human hair (and nail) length is linked to keratin levels which would account for the variety ( do Asians have more keratin? - certainly seems to be a lot of Asian women with exceptionally long hair) but in my experience of cats and dogs, they shed their hair in complete lengths.

Curly hair isn't shaped by the hair follicle as such, but rather by how friendly the sulphur in your hair is. Where it likes to hold hands, it makes your hair curl.

I've got sulphur in my body?!

Testosterone is at least partially responsible for baldness in males (in females too perhasp?), which is odd, as from experience you won't get any facial hair grow if you've not got any Apparently its to do with androgen receptors on certain hair folicles, but not on others... But, then again, a lo t of male patturn baldness is inherated sex-linked from one's mother apparently though from what I gahter, its a very multi-factored genetic thing