# Why have humans "de-evolved" hair? **URL:** \ **Category:** Factual Questions\ **Created:** [April 20, 2003, 4:13am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780 "2003-04-20T04:13:34Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Kelsonk](https://avatars.discourse-cdn.com/v4/letter/k/df705f/32.png) [@Kelsonk](https://boards.straightdope.com/u/Kelsonk)\ **Post date:** [April 20, 2003, 4:13am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/1 "2003-04-20T04:13:34Z")
I understand that we still have hair, but why has the amount that we have declined since our ape ancestors? What advantages does less hair give us? ---
**Author:** ![Random](https://avatars.discourse-cdn.com/v4/letter/r/57b2e6/32.png) [@Random](https://boards.straightdope.com/u/Random)\ **Post date:** [April 20, 2003, 4:20am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/2 "2003-04-20T04:20:15Z")
Hair costs energy to produce. ---
**Author:** ![lite](https://avatars.discourse-cdn.com/v4/letter/l/b5ac83/32.png) [@lite](https://boards.straightdope.com/u/lite)\ **Post date:** [April 20, 2003, 4:36am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/3 "2003-04-20T04:36:05Z")
Selective breeding. Think back thousands of years when a “freak” may have been born with less body hair then the norm. If this caused more procreation than normal, those genes would be passed on. And unless you’re French, you’d probably prefer a non-hirsute mate. ---
**Author:** ![Astroboy14](https://avatars.discourse-cdn.com/v4/letter/a/df705f/32.png) [@Astroboy14](https://boards.straightdope.com/u/Astroboy14)\ **Post date:** [April 20, 2003, 5:23am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/4 "2003-04-20T05:23:06Z")
Humans have “de-evolved” hair? I wish someone would convey this information to my back, nostrils and ears! ---
**Author:** ![Regina](https://avatars.discourse-cdn.com/v4/letter/r/d78d45/32.png) [@Regina](https://boards.straightdope.com/u/Regina)\ **Post date:** [April 20, 2003, 5:23am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/5 "2003-04-20T05:23:44Z")
> [@](#): > > The loss of body hair is a method of facilitating persperation [Univertsity of Waterloo](The loss of body hair is a method of facilitating persperation, and the architecture of the human hands reveals that they are better suited to climbing than swimming. ). Sounds reasonable, but should you trust a site that misspells perspiration? > [@](#): > > A major difference between humans and other primates is the great reduction of body hair in humans relative to other primates. The question of this difference has often been asked in the context of the loss of human hair, but this is not strictly true. Modern humans are not hairless in the sense of being glabrous, but rather have had a significant diminution of body hair length and thickness relative to other primates. The only hair structure that has been truly lost in the human condition is the vibrissae, which are the sensory whiskers that are common in most mammals (Van Horn 1970). > > Although hair can impede heat loss through sweating, it is important in thermoregulation for maintaining body heat in either colder environments or at night and for the reflectance of solar radiation away from the body. Dense hair cover is very efficient for both of these purposes, and it is an important question to ask why the selection for increased sweating efficiency for heat loss would be more important than the selection for the heat retention mechanism of hair cover and the heat prevention mechanism of solar radiation reflectance. Dense hair cover is an effective heat retention device, but only in smaller animals. As animals in increase in size, the effectiveness of hair cover decreases. This is due to the reduced ratio of skin area to volume as mass increases. As body size increases, the amount of metabolically derived heat increases dramatically, but the ability of the organism to effectively lose this heat is retarded by the decreased ratio of surface volume. Thus, the percentage of heat lost to the environment by conduction decreases, simply because the organism loses the ability to lose heat as size increases. This means that the hair cover is less and less evolutionary meaningful for the retention of body heat. > > The obvious solution to this situation is decreased body hair with increasing body size, which is exactly what is seen in anthropoids. From [modernhumanorigins.com](http://www.modernhumanorigins.com/anth501.html). **lite** , are you saying primitive women would have been more receptive sexually to less hairy men? Why would this be? I searched for, but could not find, the Perfect Master’s opinion on this, although he has discussed why we [still have thick hair in some places](http://www.straightdope.com/classics/a1_064a.html). ---
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [April 20, 2003, 5:40am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/6 "2003-04-20T05:40:47Z")
Why then the variation in hair among the “races”? ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [April 20, 2003, 8:29am UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/7 "2003-04-20T08:29:04Z")
In anthopoids yes, but other big animals like bears still have thick fur, AFAIK this is because the complex primate brain is more vulnerable to overheating. ---
**Author:** ![Lodrain](https://avatars.discourse-cdn.com/v4/letter/l/c4cdca/32.png) [@Lodrain](https://boards.straightdope.com/u/Lodrain)\ **Post date:** [April 20, 2003, 6:07pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/8 "2003-04-20T18:07:48Z")
> [@](#): > > \*Originally posted by Sock Munkey \* > \*\*In anthopoids yes, but other big animals like bears still have thick fur, AFAIK this is because the complex primate brain is more vulnerable to overheating. \*\* Ehh, although the brain does use a lot of energy and thus, emits a lot of heat for its size, I don’t think that we humans lost our hair because it’d overheat our brains. If that were true, then baldness would be a lot more common and I’d have scrambled eggs in my skull in place of grey matter. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [April 20, 2003, 6:51pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/9 "2003-04-20T18:51:14Z")
It’s not that our brains generate a lot of heat it’s that our brains are very vulnerable to damage from heat. ---
**Author:** ![Reeder](https://avatars.discourse-cdn.com/v4/letter/r/c6cbf5/32.png) [@Reeder](https://boards.straightdope.com/u/Reeder)\ **Post date:** [April 20, 2003, 7:01pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/10 "2003-04-20T19:01:02Z")
I’m not sure that we have. I have read that we have the same amount of hair follicles per square inch as the great apes. It’s just that their hair is thicker. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 20, 2003, 7:14pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/11 "2003-04-20T19:14:49Z")
Reeder: Not thicker in the apes, longer. We do have, roughly, the same number of hair follicles per sq inch as chimps. And the density of hair follicles on differnet parts of the body is very similar. No one knows for sure why we evolved to be more or less hairless, much less why that hairlessness various among existing humans, geographically. As for the former, I’ve seen these thoeries. Choose the one that makes most sense to you: 1. Aquatic Ape theory. Humans lost hair for similar reasons that other marine mamals tend to be hairless (ignores obvious examples like otters and fur seals). 2. Better to regulate heat in the hot African savanah. You’d kinda expect to see a bunch of other hairless savanah dwellers if this were the sole reason. 3. To highten sexual pleasure and increase the pair bond. I think this was one of Desmond Morris’ theories. ---
**Author:** ![chigger](https://avatars.discourse-cdn.com/v4/letter/c/7bcc69/32.png) [@chigger](https://boards.straightdope.com/u/chigger)\ **Post date:** [April 20, 2003, 7:29pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/12 "2003-04-20T19:29:20Z")
Not from any particular scientific study, but just on basic human behavior, at least that I’ve seen in 40 or so years: If we start with two basic premises: 1) evolution & “de-evolution” have been and are largely driven by mate selection and 2a) male primates select strongly on visual stimuli and 2b) female primates select strongly on the (apparent) ability of the male to provide food & shelter. So, these lead to a couple of hypotheses: Hypothesis A: A female with a genetic aberration resulting in greater exposure of genitalia is more likely to be selected by males. Hypothesis B: A male with less fur insulation stood a better chance of survival if he was industrious and cerebral enough to concoct a means of warmth, such as harnessing fire, taking pelts of other animals, and/or finding more food, all of which would be viewed as providor traits (as opposed to just lolling about in their own fur, eating berries). Or some combination of the two. ---
**Author:** ![Fretful\_Porpentine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fretful_porpentine/32/2873_2.png) [@Fretful\_Porpentine](https://boards.straightdope.com/u/Fretful_Porpentine)\ **Post date:** [April 20, 2003, 7:42pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/13 "2003-04-20T19:42:56Z")
I have a hard time believing that sexual attraction would be a factor, because removing hair isn’t exactly high technology. If all the females prefer less-hairy males, or vice versa, you’re more likely to see a lot of males who pluck or shave themselves rather than a bunch of hairy males who don’t get to breed at all. I’d vote for the perspiration theory in the absence of better ideas. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 20, 2003, 8:54pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/14 "2003-04-20T20:54:54Z")
Actually, I’d vote for the fact that humans are neotenous apes: we retain into adulthood features which in other apes are present only in juveniles or earlier. Human babies are, for the most part, comparitively fetal when born, even relative to many other apes. And fetuses are not known for being hirsute. Mammals such as dogs and cats are typically born relatively hairless as well (and are similarly fetal in appearance and capacity). They eventually acquire thick coats, while we simply retain that hairless state. There was not necessarily any functional aspect to the loss of hair, it was simply associated with the particular direction our evolution took. ---
**Author:** ![monica](https://avatars.discourse-cdn.com/v4/letter/m/a183cd/32.png) [@monica](https://boards.straightdope.com/u/monica)\ **Post date:** [April 20, 2003, 9:01pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/15 "2003-04-20T21:01:46Z")
I think it’s the Aquatic Ape Theory. Basically, this says that we evolved near/in the water, probably on the coast of Africa. Basically, hair would slow us down as we were swimming through the water. Those with more hair would become the victims of predators, while those with less would escape. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 20, 2003, 9:34pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/16 "2003-04-20T21:34:44Z")
Darwin: Interesting thought. I’m immediately hit with a couple observations that might challenge the neoteny theory. 1. Newborn chimps don’t seem to be particularly hairless. Same with pictures of chimp fetuses I’ve seen. 2. Human fetuses generally grow a coat of longish, fine hair that is shed before birth. If it was neoteny, wouldn’t that stage be supressed or skipped altogether? I think of neoteny as the retention of earlier triats, not a process that produces certain traits, then discards that trait. Comments? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 20, 2003, 9:43pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/17 "2003-04-20T21:43:11Z")
> [@](#): > > _Originalliy posted by monica_ > **I think it’s the Aquatic Ape Theory.** The “Aquatic Ape Theory” is one of the more ludicrous “just so” stories which attempt to explain our evolution. It has very little (if any) supporting evidence, and is based entirely on the flawed premise that every trait is necessarily adaptive in nature. Many of the reasons why this so-called theory still persists, despite this lack of supporting evidence, can be found [here](http://aquaticape.topcities.com/whyanthro.html). [Another page on the same site](http://aquaticape.topcities.com/hair.html) lists some reasons why the AAT fails as a reasonable explanation for our relative hairlessness. ---
**Author:** ![KellyM](https://avatars.discourse-cdn.com/v4/letter/k/57b2e6/32.png) [@KellyM](https://boards.straightdope.com/u/KellyM)\ **Post date:** [April 20, 2003, 9:52pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/18 "2003-04-20T21:52:11Z")
It is possible that it was just a random mutation that occured along the way that provided no direct survival benefit, but that just happened to correspond to some other mutation that did. Not all evolutionary changes are beneficial; some are neutral and others detrimental, but survive on by pure happenstance. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 20, 2003, 10:05pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/19 "2003-04-20T22:05:04Z")
> [@](#): > > \*Originally posted by John Mace \* > **Darwin:** Call me Finch. I’m no Darwin. 🙂 > [@](#): > > **1. Newborn chimps don’t seem to be particularly hairless. Same with pictures of chimp fetuses I’ve seen.** To be honest, I’ve never seen a chimp fetus, so I can’t say one way or another. However, one of the primary aspects of neoteny is that development is greatly slowed down in the neotenous species, relative to its ancestors. Obviously, we humans are not devoid of hair, we simply do not grow the luxurious coats that our ape relatives do (well, most of us don’t, anyway). Similarly, chimps and other apes do not begin with those fur coats - as the fetus develops, the length of the coat will increase. We prolong this process to an excruciating degree (even at 33, I notice I have thicker body hair than I did ten or even 5 years ago). Humans begin growing hair at about 5 months, if I recall correctly. However, during the ensuing four months prior to birth, the rate of growth of this hair tends to remain low, whereas in chimps the rate of growth is higher (to the point where the newborn may well have a full coat). This would appear consistent with a neotenous origin: the rate of hair growth is greatly reduced relative to other apes, and remains so throughout our lifespan. > [@](#): > > **2. Human fetuses generally grow a coat of longish, fine hair that is shed before birth. If it was neoteny, wouldn’t that stage be supressed or skipped altogether? I think of neoteny as the retention of earlier triats, not a process that produces certain traits, then discards that trait.** I am not familiar with this fact. Can I get a cite? It would seem to me that _any_ explanation would tend to falter if that is, indeed, the case. That is, even if one were to argue for an adaptive cause for our hairlessness, the growth of a pre-birth coat of hair which is then lost, still prior to birth, would not seem to represent any adaptive fucntion, either. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [April 20, 2003, 10:07pm UTC](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780/20 "2003-04-20T22:07:13Z")
> [@](#): > > \*Originally posted by Darwin’s Finch \* > **However, during the ensuing four months prior to birth, the rate of growth of this hair tends to remain low, whereas in chimps the rate of growth is higher (to the point where the newborn may well have a full coat).** To clarify: the rate of growth of _body hair_ remains low. Many infants are born with a full head of hair, indicating that hair growth on the head appears to proceed at “normal” rates. [Next page](https://boards.straightdope.com/t/why-have-humans-de-evolved-hair/169780.md?page=2)