Ape haircuts?

June 2, 2007 5:02 AM

Why don't apes need haircuts?

I had a haircut today. If I'd left it, it would have grown longer. Sitting there, it occurred to me that chimps, gorillas, etc. don't have haircuts, but why? Does their hair moult (and why doesn't mine then?) Do the long hairs get groomed out by other apes? What happens to apes living alone then?

posted by A189Nut to Pets & Animals (27 answers total)

You hair does moult, every time you brush your hair you get rid of the loose ones. Even if you don't brush your hair, they still fall out.

Also, apply the same question to your body hair. Does *it* need a hair cut? I doubt it.

I've always assumed that hair (and fur) has a set length, a limit it can't go beyond. In my mind this explains why some people can have masses of glorious hair whilst others can't get it to grow below their shoulders.
posted by esilenna at 5:13 AM on June 2, 2007

Quite a lot of information on both moulting and growth/dormancy to be found on the hair article of Wikipedia
posted by esilenna at 5:15 AM on June 2, 2007

Humans have hair that grows in cycles, and over time can get very long. Animals have fur that grows to a certain length and stops.
posted by hortense at 5:37 AM on June 2, 2007 [1 favorite]

See also: why your cat does not need a shave
posted by briank at 7:23 AM on June 2, 2007

The real question, I think, isn't why apes don't need haircuts but why humans do. We appear to be unique in the animal kingdom in that we have all this stuff growing out the top of our heads.

It's been a while, but I seem to recall that Desmond Morris suggested that a mane of hair gives a savannah ape, standing on two legs, a unique profile that can be recognised from a distance.
posted by Leon at 8:28 AM on June 2, 2007

There was an interesting discussion of this topic on a recent episode of Fresh Air. The conclusion was that we don't really know -- that head hair is pretty unique, but often grooming is an important social function, so it may have had to do with that.
posted by YoungAmerican at 8:47 AM on June 2, 2007

For you evolutionary biologists: does every little quirk and feature need to have an instrumental reason for being? Maybe some things, such as hair that keeps on growing, have no purpose whatsoever -- they're just incidental artifacts of the process. They haven't helped the species survive nor harmed it's chances and so nature has had no reason to edit them out.
posted by notyou at 9:08 AM on June 2, 2007

Also see The Straight Dope columns: Why does head hair grow indefinitely but other body hair doesn't? and How does body hair know it's been cut and grow back?.
posted by IvyMike at 9:36 AM on June 2, 2007

For you evolutionary biologists: does every little quirk and feature need to have an instrumental reason for being?

No.
posted by docgonzo at 10:07 AM on June 2, 2007

so nature has had no reason to edit them out.

I agree with "no." Keep in mind that evolution is something that happens- strong animals survive to breed, weak ones don't. In general, this leads to evolution, but it's an incredibly slow process, and it's also very random in a certain sense.

I always find this odd: people who are pro-evolution are by definition anti creationism and intelligent design. yet they tend to personify "nature" or "evolution," as if there is someone with a finger on the trigger, deciding how to make the best animals. No one is "editing" or "changing" anything. it's just happening.
posted by drjimmy11 at 10:20 AM on June 2, 2007 [1 favorite]

For you evolutionary biologists: does every little quirk and feature need to have an instrumental reason for being?

armchair one here: no, but sexual selection is an immensely important force over the past 50,000 generations or so.
posted by Heywood Mogroot at 10:26 AM on June 2, 2007

I believe it was this NPR story that talked about how hair became important in human evolution, including the origins of homo sapiens culture and language. I'll keep looking to make sure.
posted by nax at 11:26 AM on June 2, 2007

For you evolutionary biologists: does every little quirk and feature need to have an instrumental reason for being?

Yes.

Maybe some things, such as hair that keeps on growing, have no purpose whatsoever -- they're just incidental artifacts of the process.

Things that have no purpose cost energy to be created. Hair doesn't grow by itself. It costs calories. The organism is expending energy on something. There are three possible reasons: a) it's been evolutionarily selected; b) it's a mutation that will be selected out of the gene pool at some point in the future (and remember, we're talking a huge swath of time here, so it won't happen next week); or c) it's a vestigial thing that was previously important for some reason that we're currently blind to (like your appendix, or Heywood's comment about sexual selection) and is now will eventually be selected out.

Stuff doesn't just happen for the hell of it. And if it does, an organism competing for the same limited resources that doesn't waste energy, and instead expends energy on something that is more useful over the long term, will be selected.
posted by frogan at 11:31 AM on June 2, 2007

I'm going to go with conservation of heat....That we lose a large percentage of heat through our heads - and we're the 'hairless' ape - that our naked bodies went hand in hand with the creation of clothing.
posted by filmgeek at 11:38 AM on June 2, 2007 [1 favorite]

Oh, and nevermind the fact that in the wild, our Cro-Magnon forebears were probably killed by sabretooth lions long before the ever-growing hair became a problem ... or perhaps it was the long hair in the eyes, obscuring vision, that caused us to be killed by the sabretooths...? And perhaps it was the high rate of sabretooth deaths that led Thog and the tribe to develop tools to kill the sabretooths...?
posted by frogan at 11:50 AM on June 2, 2007

Male lions have longer hair. (sorry, I had to point it out when someone said that we are unique). It is not ever-growing, but it still is longer on their neck/head.
posted by nursegracer at 12:39 PM on June 2, 2007

Head hair is so central to sexual attractiveness in all cultures and all time periods I have enough information to make any kind of judgement about, for both men and women, and it is at the same time so variable in ways that are genetically determined, and so potentially detrimental in so many circumstances when it is long, I don't see how the fact that it can grow to great length in most individuals could possibly be "incidental."

If you want an idea of how detrimental hair can be, imagine being in a life or death fight, or a fight which will determine your place in the hierarchy, with another human being if you have shoulder length hair and they have a burr, or imagine being pursued by a pack of hyenas and what will happen to you if one of them gets hold of your long hair.

Long hair is enough of a problem, in fact, that I think we must give at least a nod to the hypothesis that it is a Fisherian Runaway, like the peacock's tail, or an example of the handicap principle, which asserts that individuals who have an obvious handicap such as long hair or, again, the peacock's tail, and are alive and healthy even so must have a genetic endowment that is otherwise desirably superior in order to allow them to overcome the handicap, and therefore are to be preferred as mates.
posted by jamjam at 12:53 PM on June 2, 2007

Things that have no purpose cost energy to be created. Hair doesn't grow by itself. It costs calories. The organism is expending energy on something.

Of course it uses some energy, but, especially in our cushy lives that permit us to post to MeFi instead of roaming the plains hunting for tonight's meal, do the calories used for hair growth really cost us much? (It's also not as if most Americans have a deficit of calorie intake...)

If anything, I'd wager that bald people are less likely to find a 'partner' to reproduce with, ergo those with the "defect" of unceasing hair growth on the head perpetuate.
posted by fogster at 1:05 PM on June 2, 2007

If you want an idea of how detrimental hair can be, imagine being in a life or death fight, or a fight which will determine your place in the hierarchy, with another human being if you have shoulder length hair and they have a burr, or imagine being pursued by a pack of hyenas and what will happen to you if one of them gets hold of your long hair.

This is why I shave my head.
posted by j-urb at 1:13 PM on June 2, 2007 [1 favorite]

but, especially in our cushy lives that permit us to post to MeFi instead of roaming the plains hunting for tonight's meal, do the calories used for hair growth really cost us much?

You're kinda falling into a trap that many people fall for -- the conceit that "now" or even "recent time" has any bearing whatsoever. Humans are mammals. Mammals have hair. Modern humans have been around for thousands of years. Mammals have been around for millions of years. Now is utterly meaningless. One hundred years ago is meaningless. It's only in the aggregate that you can make any determinations.

Just because it doesn't seem to make sense now, or that calorie expenditures to grow hair seem low to you (it's actually not low at all -- skin, hair and keratin are pretty important structures and take up significant energy), or otherwise fails to fit within the framework of our current condition, doesn't mean evolution as a concept falls apart, as if you pulled out the one important keystone.

I'd wager that bald people are less likely to find a 'partner' to reproduce with, ergo those with the "defect" of unceasing hair growth on the head perpetuate.

You're upside down. Evolution is ruthless. If there is something that is preventing you from passing on genes, that is the defect. Or it will soon become one. Or rather, if hair = sex, then lack of hair either = no sex or = a marker of some other mechanism that facilitates the male pattern baldness gene being passed along. Maybe the bald guys are smarter than the hairy ones? ;-)
posted by frogan at 1:30 PM on June 2, 2007 [1 favorite]

Long hair on human heads may be the side-effect of some other gene mutation that is very desirous. For example, the same gene(s) that allow us to have the vocal structure we use may also cause our hair pattern and growth. I just made that up, but you can see where being able to speak is worth the energy it takes to maintain long hair and the hazards it creates.

A subsequent bias towards seeing long healthy hair as an indications of gene health may be something that evolved as well after the fact.

Like posters have stated above, it is likely that hair length in and of itself was not the point, but rather it is what has won out in a multitude of potential outcomes because (so far) it has helped propagate the species well enough.
posted by qwip at 2:51 PM on June 2, 2007

My guess would be that long, luxurious hair is sexually selected. It's a display of health and success. Anyone with a long, healthy mane of hair is someone who is eating well, not diseased, etc.
posted by empath at 6:08 PM on June 2, 2007

Who says they don't?
posted by rob511 at 8:32 PM on June 2, 2007

Don't horses have long, luxurious hair that grows out of only certain parts of their bodies, and that grows back if you cut it? It's not only humans.
posted by croutonsupafreak at 10:43 PM on June 2, 2007

I believe I have observed that head hair becomes much thicker and more luxurious on both boys and girls at and a little before puberty (perhaps at adrenarche?) and tends to thin at menopause and, interestingly, during pregnancy, and even in men without male pattern baldness in their 50s and 60s.

It's tempting to guess, in that light, continuous hair growth could have to do with the absence of a breeding season in humans; continuous estrus, as I have seen it described, resulting in continuous hair growth, and possibly being part of the program of concealed ovulation among humans, but I'm embarrassed to say I don't know if that absence of a season is unique to humans among the primates.

Don't horses have long, luxurious hair that grows out of only certain parts of their bodies, and that grows back if you cut it?

They have such hair in their tails and somewhat in their manes, I've read; explained in their tails as a means of switching horseflies away from settling long enough to bite, and maliciously cut by the evil boys of my childhood animal stories as a form of torture. In their manes, I'm not sure what it's thought to be for. Perhaps the stallion grips it when he mounts the mare, providing her with a means of testing his teeth while she evaluates his mettle in other respects.
posted by jamjam at 5:59 PM on June 3, 2007

Head hair probably does have a set length. I wanted to grow my hair long in my teens (female classmates had long flowing tresses), but it stubbornly refused to grow further than my shoulders. It is very thick, so its potential for growth is probably going into density.

This was decades before I read the post about freakishly long hair which appeared in MeFi a while back.
posted by bad grammar at 8:04 PM on June 5, 2007

I got into a comparative discussion of religion with one of my high school classmates once, wherein I learned she belonged to a pentecostal sect that prohibited women cutting their hair. I observed that hers did not appear to be dragging on the floor—it was mid-back, which is longer than average, but nothing remarkable. She said your hair has a natural length to which it grows, determined by the rate your follicles produce it at and the length of the grow-hold-shed cycle on which they operate.

Most people don't think of themselves as shedding because the follicles are not naturally synchronized. Sometimes they get synchronized by hormonal birth control, whereupon the newly birth-controlled woman goes to her doctor worried that all her hair is going to fall out.

Oh, and j-urb: Alexander the Great insisted that his troops shave their beards as their last preparation for battle with the Persians. You are in good company.
posted by eritain at 10:05 PM on June 5, 2007