Long hair a human-only trait?

The hair on our heads grows quite long, as does male facial hair, and when trimmed it keeps growing back. Is this a strictly human trait? Any theories as to why our hair grows long besides the one about us once being aquatic and the hair gave our babies someting to hang onto?

It’s a secondary sex characteristic.

Horses and lions have long hair as well.

Probably so. See male lion manes.

But theirs stops far shorter than ours.

No, it’s not. Secondary sex characteristics differentiate the sexes, but both men and women can grow long head hair.

The OP can correct me if I’m wrong, but I believe his question is not specifically about the length of the hair, but rather the fact that it grows indefinitely.

I just (yesterday) cut the hair on my Bichon Frise pooch. It’s hair, not fur, and it was getting mighty long. Bichon’s don’t shed: they’re hair dogs. I think poodles fall into the same category.

Right, Q.E.D.

A lion’s mane doesn’t keep growing to the point where he’s tripping over it. And while male facial hair may be considered a secondary sex characteristic, it, too, can grow to an unwieldy length.

That’s not a theory. It’s a fairy tale.

It is very, very rare for human hair to grow indefinitely. For the vast majority of humans hair length is determinate. The hair grows for a set period and then falls out, resulting in a mane of determinate length.

The idea that every single woman can grow hair down to their ankles if they don’t cut it for long enough is myth.

Some breeds of dogs have (potentially) very long hair. Examples? Afghan Hounds and Old English Sheepdogs. I think this is also true of Maltese and some other Toy breeds, but am not entirely certain. My knowledge of breeds outside the Working and Hound groups is limited. An Afghan that is maintained for showing in conformation is likely to have some body hair that sweeps the ground. Groomers would, of course, trim that; it would pick up too much dirt, and the owners and/or handlers already put an enormous amount of work into keeping the coat clean and shiny, but if you look at photos of show Afghans, you’ll see that their coat just barely clears the ground. I know that the fringes on some Salukis (hair on the ears, backs of legs, and tail) will grow very long, depending on bloodlines. Show dogs are generally kept in climate-conditioned environments, so that they don’t “blow coat” (shed) twice yearly. It’s hard to avoid that with a female you’re breeding, but there are tricks to keep them from shedding very much when they whelp.

It may also be true of some of the long-haired cat breeds, but I know significantly less about purebred cats than I do about dogs. And given that cats groom themselves, and make hairballs thereby, it seems to me that maintaining a longhaired cat for showing would be a monstrous PITA. Where horses are concerned, AFAIK, the only coat that grows more or less continuously is the mane and tail, and it’s variable, depending on the breed of horse. ISTR seeing photos of musk oxen with coats which came awfully close to sweeping the ground, but that would be their winter coats, not the summer ones - and bear in mind that they shed out twice a year. But very long, very dense coats are a survival characteristic for them, after all. There seems to be some evidence that the hair on mammoths could also grow extremely long - of course, the evidence on them is limited mainly to remains that have been discovered, since they died out around the beginning of recorded history, and not near areas where writing was coming into use.

Perhaps you are not aware that not all ethnicities of humans are able to grow hair that’s very long. Most people of pure sub-Saharan African ancestry have hair (on the head) that will grow only a few inches. This is also true of those Melanesians who have a different kind of “kink” in their hair (spiral, rather than like a sinusoid spring). Some ethnicities - many different kinds of Asians, and pretty much all of the peoples native to the Americas - are able to grow hair significantly longer than the average. It’s only the men of some Plains nations (particularly the Lakota) who grow their hair long, but I recall seeing one man whose hair was longer than he was tall. He wore it in a ponytail, and had it caught up in the middle so it didn’t drag. And it is not at all unusual for women from the Indian subcontinent to be able to grow their hair longer than their height. Some women of some European ethnicities are able to grow their hair to their hips or knees, but this isn’t the average; the average is around waist-length.

Data on men’s hair is very sparse; after all, most men don’t even try to grow either their hair or their beards very long. However, it seems that most men who are able to grow beards can grow their beard longer than their hair.

Again, nobody keeps data on this stuff. What I’m telling you is the result of observation - not at all ideal for GQ, but the best I can do. Some of it (e.g., hair growth patterns on African and Melanesian people) is stuff I learned in anthro and/or biology classes, however.

The Friesian horse’s mane & tail can grow quite long.


Obligatory link to a Komondor picture.

[tangent]I always learned that “secondary sex characteristic” refers to those traits gained at puberty. The example I remember from high school biology class is pubic hair, which, by your definition is not a secondary sex characteristic. Looking over the wiki, the article seems to agree with your definition, but the talk page for that article brings up my definition. This point, unfortunately, is lost in the fracas over the nudie pics on the page. Q.E.D., I believe your definition is more suitable for the term “sex characteristic”. [/tangent]

WhyNot, FarmerChick, tygerbryght, and Leaffan: I don’t want to speak for the OP, but I’m assuming the question is really asking about why we evoloved this way. Discussions of specific breeds of dogs or horses are probably irrelevant as examples of artificial selection, not evolution.

Right. And I understand that why we evolved that way is not a question that’s easily asnswered.

I’m wondering if there are any theories, more accepted than the widely discredited aquatic development one, which account for long head hair being selected.

And comparision to horses and dogs, while interesting, does not explain why apes seem not to have beards or long hair.

No. Hence the pictures of the horse.

It’s like Cher was turned into a horse!

Who knew dreadlocks were part of a WKC standard?

Natural selection. Because a lot of guys evolove girls with long hair.

But gorilla and chimp guys don’t like long hair?

The only thing keeping men’s hair short is scissors.