On why (some) humans have lost their body hair? Why are we the only hairless primate?
In case you have forgotten, humans have relatively hairless bodies when compared to our other great ape relatives, even to the 5,000 or so other mammalian species out there. This is curious phenomenon — we seem to defy the very classification of being a mammal.
Sure, there’s a lot of variation among human populations. Some of us are hairier than the others, while others of us aren’t. There are even known genetic ‘mutations’ that reverse our hairlessness into a ‘werewolf syndrome’ which is known in science as hypertrichosis. 
Fajardo Aceves Jesus Manuel of Mexico is a modern day example of someone with hypertrichosis. This condition is caused by a genetic defect that,
“causes the hair growth cycle in victims of this rare disease to run amok. The follicles from which the body hair grows are apparently incapable of switching from the growth phase to the dormant phase, which normally ends in the new hair falling out and the cycle begining again.”
Hypertrichosis is considered an atavism — or an evolutionary throwback. An atavism is a trait that reappears which had once disappeared generations ago. This happens mostly likely thru a backward mutation but it can also happen thru transposable elements within the genome, i.e., the ‘hairy gene’ was locked away in a region of the genome that was not expressed but then was shuffled and inserted into an expressable region. Other known atavisms occur thru this mechanism. Genes that coded for a previously existing phenotype are often preserved in DNA, even though the genes are not expressed in some or most of the organisms possessing them.
But hypertrichosis is a rare genetic disorder, actually it is very rare. Only about 50 cases of the condition have been documented since the Middle Ages. That indicates there has been a strong positive selection to keep us hairless. But why? Are there any evolutionary explainations as to why humans are hairless?
Well, there are three main stories explanations (?) for why humans lack fur. Scientific American has asked an expert, Mark Pagel, head of the evolutionary biology group at the University of Reading, and he summarizes these hypotheses for us. These hypotheses vary in evidence but they all revolve around the idea of a positive selective pressure to not be hairy. In other words, it may have been advantageous for the human lineage to have become less and less hairy during the six million years since we shared a common ancestor with our closest living relative, the chimpanzee.
The first hypothesis, named the ‘aquatic-ape hypothesis’ considers that way back in the day, like 8 million year ago an apelike ancestor of modern humans had,
“a semiaquatic lifestyle based on foraging for food in shallow waters. Fur is not an effective insulator in water, and so the theory asserts that we evolved to lose our fur, replacing it, as other aquatic mammals have, with relatively high levels of body fat. Imaginative as this explanation is—and helpful in providing us with an excuse for being overweight—paleontological evidence for an aquatic phase of human existence has proven elusive.“
I was taught that our hairlessness initially came about from an adaptation that occurred as apes moved down from the jungles and into the hot savanna. Hairlessness helped control our body temperature when hominids made the transition to a new ecosystem.
“Our ape ancestors spent most of their time in cool forests, but a furry, upright hominid walking around in the sun would have overheated.”
This theory seemed to make a lot of sense, when I was taught this by my professors. However, it had one major flaw. The lack of fur,
“might have made it easier for us to lose heat during the day, [but] we also would have lost more heat at night, when we needed to retain it.”
A recent theory, one that I briefly introduced on Primatology.net back in March, considers that ancestors to modern humans were selected be hairless as a means,
“to reduce the prevalence of external parasites that routinely infest fur. A furry coat provides an attractive and safe haven for insects such as ticks, lice, biting flies and other “ectoparasites.” These creatures not only bring irritation and annoyance but carry viral, bacterial and protozoan-based diseases such as malaria, sleeping sickness, West Nile and Lyme disease, all of which can cause chronic medical problems and, in some cases, death. Humans, by virtue of being able to build fires, construct shelters and produce clothes, would have been able to lose their fur and thereby reduce the numbers of parasites they were carrying without suffering from the cold at night or in colder climates.
Human lice infections, which are confined to the hairy areas of our bodies, seem to support the parasite hypothesis. Naked mole rats, animals that can be described as resembling “overcooked sausages with buck teeth,” also seem to support the theory: They live underground in large colonies, in which parasites would be readily transmitted. But the combined warmth of their bodies and the confined underground space probably negate the problem of losing heat to cold air for these animals, allowing them also to become naked.
Once hairlessness had evolved this way, it may have become subject to sexual selection—being a feature in one sex that appealed to another. Smooth, clear skin may have become a signal of health, like a peacock’s tail, and could explain why women are naturally less hairy than men and why they put more effort into removing body hair. Despite exposing us to head lice, humans probably retained head hair for protection from the sun and to provide warmth when the air is cold. Pubic hair may have been retained for its role in enhancing pheromones or the airborne odors of sexual attraction.”
Will we ever know why hairlessness was selected for in our lineage?
No, just like we may never really know why bipedalism was selected for in our lineage.
But the problem with hairlessness versus bipedalism, is that hairlessness is one of those wild witch hunts that we embark on, one that relies on story telling and a whole lot of what-if’s. It is full of conjecture and not much scientific evidence. Regardless of its flaws, this question remains a very thought-provoking one to me, as someone interested in physical anthropology.
After writing this, I consider hairlessness could have been due to a founder-type effect. Since no supportable physiological significance can be drawn at this time, what if hairlessness became dominant a dominant allele because people who carried the hairless recessive mutant allele replaced people carrying the dominant hairy allele after a population bottleneck?
Again another what-if, however it is a plausible evolutionary possibility… But is it supportable?
No, not at this time… unless we figure out when this allele was really prevalent in our populations after a certain time and correlate its switch from recessive mutant to a dominant after some bottleneck inducing phenomenon, like an epidemic that targeted hairy people more. Until we sequence more paleoDNA from other hominids (mind you we can only extract nuclear DNA from Neanderthals, as of now) this hypothesis is also just as outlandish & unsupported as the aquatic ape one.
All these theories are interesting, but my Gran who was born to British parents, with Dutch back to the 1500′s, and nothing else that stands out as being Asian, North American Indian or other , was completely hairless from her head down. Her eyebrows were thin and her complexion leathery but she was old. My father consequently has hardly any hair on his body except his head, whilst my brother and I have hardly any leg or arm hairs, fine head hair with some areas having noticeably less follicles. My children however appear to take after my husband and have what I would consider ‘normal hair growth’. Although one child is much less hairy than the other.
So does this mean that there Must be some gene that is not working correctly, or perhaps my Gran was the milkmans and not my Great Grandads! Unfortunatley due to the death of her relatives, other than one surviving brother, I do not know if my Gran was unique in her family, or if one or both parents held this defective gene.
This is NOT alopecoa, as in gradual hairloss such as Gail Porter,, this is genetic within my family, my very European family. Although there are some gaps within my family tree where the male relatives were Sea Captains who did travel to the Carribean, so it is possible to have picked up some different nationality relatives, and my Grans condition was obviously severe whereas mine is somewhat muted.
I have found all your comments very interesting in trying to decipher why we are much more hairless than other Europeans. However, none of the answers really explain why different races have different traits, one can oly assume that evolution in the same mode as size or skin colour is to blame!
Mich
November 29, 1999 at 4:00 pm
It seems as if adaptations for hairlessness could have arisen as we began living in closer proximity and in larger groups during the Neolithic. There was an increase in infectious disease during this time, so it seems as if a loss of body hair could have somewhat somewhat offset an individual’s chance of being infected during this transitional period. Of course, this would mean that the loss of body hair was a relatively recent occurrence…
Robert
June 11, 2007 at 1:45 pm
Right on Robert, yeah I think the Neolithic coulda been one of the times where hairlessness was selected for. I think you are onto something. The Neolithic transition was a critical shift, and could manifest founder-effect selection.
Again, the problem still remains to find out when did was this mutation introduced into our genome… Until we find out, this and all the other theories are very speculative.
Thanks for commenting!
Kambiz
June 11, 2007 at 5:18 pm
Kambiz, any comment on this?
I’ve an OT question that relates to dinosaur feathers and hominid hair.
When hominid researchers in the field find a skull, what is their priority? To pick and brush it off right? Since we know that feather imprints can be retained if the critter was covered in fine mud (rare but not unusual), shouldn’t skull diggers be looking at the inverse of the skull for hair imprints on the dried mudstone? Of course once the skull’s soft tissues decomposed, the surrounding silts or clays moving inside would destroy some of the features, but the dead hair protein would probably leave an imprint, possibly visible through MRI or micro or nano Xray analysis or something. I for one would like to know the precise hair/beard patterns, as I’m tired of paintings, drawings, models of ancient neandertals, erectoids and apiths with short haircuts, since sapiens have hair that grows a yard long when left uncut.
But then again, some people think our ancestors were like chimpanzees on savannas, where long hair is useless. I do wish the bone & stone folks would check on hair, probably the only soft tissue recognizable after 20k years in the hardening mud.
DDeden
September 27, 2007 at 2:45 pm
DDeden,
Excellent question. I don’t know of any hominin fossils that told us something about the hair patterns and density.
It could be that people aren’t careful while excavating the remains, but from my experiences, people really slow down and take it easy when they find a precious hominin fossil. I doubt that it has to be due to their priorities because there’s nothing more important than delicately removing a fossil, taking note of the context it’s coming from.
That being said, a lot of why we don’t see fossils with evidence of hair patterns from hominins has to do with the sediment and chemistry the fossil was laid down in. Not every hominin fossil is formed because it settled in ‘soft muddy sediment.’ Fossils like famous archaeopteryx one, which show imprints of feathers, are rarities. Only a certain condition would yield such a result. Many fossils are formed in different sediments, with different chemicals, pumus, and even physical dynamics that affect the ability soft tissue is imprinted.
The process to make a fossil takes thousands, if not hundreds of thousands of years, depending on the conditions. A lot can happen during that time. And it happens in different places too.
Fossilization is the process where organic compounds in bone is replaced with inorganic minerals. Often, soft tissue, like hair and the skin it grows out of, is sloughed off and removed by natural phenomenon, scavengers, etc. Other times, hair just won’t last that long. You know how thin is, to have it degrade but still yield an imprint is rare. Even the most malleable sediment will fill in and warp.
I guess the best paleoanthropologists can do, is to sample for trace elements, like degraded hair protein since that may last. I don’t think any sort of visualization technique, can, at this time, show us what you’re looking for.
I hope that answers your question.
Kambiz
Kambiz
September 29, 2007 at 9:34 pm
Neotony. I curious about that as an explanation for many of the distinctive traits we see in our fellow primates. It seems to me lately that the hairlessness that we exhibit into our adulthood is somehow allied with the suite of other expressions of neotony, traits that figure prominently in who we were and who we were to become: big heads, thin skin, cartilage growth throughout life, and covered with fat. It’s not so much that we’re hairless but that our follicles never produce hair like a normal maturing animals in the population from which we diverged. Maybe hairlessness was a genetic inevitability as a result of the way our genes work in certain relationships with other genes. So maybe big brains mean that the potential to grow a heavy pelt is proportionately reduced. At some point the lack of a hair is overcome by the emergent concept of manufactured shelter and the enhanced security of communalism. Being able to tolerate ones fellow species members becomes a requisite for success in gaining access to mates. This kind of instinct for social bonding is not uncommon in young animals but later as adults the group becomes “us” and everything else is “out there”. But in another expression of neotony, our ancestors retained their flexible/elastic social instincts into their adult lives, reinforcing the cohesiveness that provides a degree of advantage over other animals with whom they share the habitat’s resources…and as we have continued to these times.
doug l
October 10, 2007 at 3:56 pm
Why are most native americans/Indians almost hairless, no arm or leg hair, yet they have a full head of hair? Is this typical? Is this a true feature of an indian or native american?
Bobbie Neu
October 20, 2007 at 8:55 am
Bobbie,
I am mostly Indians actually over 3/4 and I have never had underarm hair. I have also heard that it is a characteristic of Native Americans.
Jena
December 21, 2010 at 8:25 pm
Bobbie Neu. East Asians generally have very little facial hair and Native Americans are presumed to have at least some East Asian ancestry. Could easily account for it. When I visited USA I met Pueblo Indians who had very sparse beards and moustaches, looked quite a bit like as Ho Chi Minh.
TerryT
October 21, 2007 at 2:00 am
The naked mole rat hairlessness as a method to reduce ectoparasites and suggested to parallel the reduction of hair in humans, is not supported. Lice are warm-body-temperature dependent, living between the skin and insulative fur; naked mole rats are virtually cold-blooded (very unlike the human metabolism). Their colonies are known to be very high in CO2 and low in O2, conditions not conducive to insects. Human ancestors were unlikely to have lived under those circumstances sustainably.
Since most terrestrial mammals thrive encased in their fur coats both in tropical and arctic climes despite associated ectoparasites, something else must have caused human body hair reduction concurrent with scalp hair extension and retention of three species of lice.
DDeden
December 19, 2007 at 4:18 pm
Here! I got another thesis!
Perhaps, with the appearance of human consciousness and therefore a specific self image/identity, our women ancestors found less hairy men more sexy, because these more resembled a physical otherness from nonhuman animals. Other animals were seen as more primitive, somehow of lower status and hence those men which more resembled nonhuman animals because of strong hairyness were also attributed with that lower status. So women at one point, because of their human sense of identity started preferring less hairy men.
Well at least that was the thing which first entered my mind 0,2 (0.2) seconds after reading the headline…
Giant Vegan Female
December 27, 2007 at 1:34 pm
Precicely my thoughts BUT why women selecting men. In primative times men selected their female partner sometimes without consent. I see a preference of less hairy females as being wifes to fight over. And as the generations progressed the outcome was substancial less hair. Pubic hair in a lot of tribal cultures was a signal of breeding age. so it remained in the both sexes
The presence of more hair in mainly european s is largely climatic. Males having full thick beards and sometimes lots of body hair. obviously the females of european stock inherit more body hair because of this.
Mike Tummon
December 29, 2011 at 9:17 pm
Obvious. Skin parasites prosper only in skin patches where there is hair. Selection favors skins that are unfriendly to parasites. Full stop.
j
January 2, 2008 at 3:38 pm
J: Whales have skin parasites yet lack hair.
Orangutans have lots of long body hair yet lack lice, humans have very reduced hair yet have 3 species of lice.
GVF: If hair reduction was caused by females preferring less hirsute males, why do males have more hair than females? And why during puberty do males get the hairiest, if that is the time of most sexual selection? It doesn’t add up. Hair reduction in most aquatic mammals does. Seems obvious to me that human ancestors spent some time day to day in seawater at the tropics, as many people do today.
DDeden
January 4, 2008 at 12:16 am
Yeah why are some better at being hairless than others? Asian/Native American/African. Could friction be part of it? Traveling through tall grass like in Africa. Native Americans are known for being able to quickly cover large ground through thick foliage. Tribes that live in thick jungles are always hairless. I’ve heard men who wear socks a lot sometimes lose hair from the sock line down….
CJONES
March 11, 2008 at 11:10 pm
CJONES, I’ve been thinking about your comment for sometime now. I don’t mean to offend you by saying it is rather humorous to think about your hypothesis.
To clarify to you and others, the real reason why ‘some are better’ at being hairless has to do with regional adaptations to temperature. Hair functions to regulate body heat. In colder areas, people are generally hairier. That’s not always the case, such as the Nepalese and Tibetan populations are relatively hairless. But in areas like the Caucuses,
Hair is also hormonally controlled. As you may have noticed, hair growth increases along with puberty. While all populations undergo puberty, different levels of hormones affect the amount of hair growth.
You may definitely be onto something, but I don’t think thickness of brush has a direct relation to hairiness. The reason why Africans are hairless is largely because most of Africa is hotter and losing hair may have been advantageous for thermoregulation. Asian populations, I dunno what’s going on with their hairlessness… but one of the reasons as why Native Americans are relatively hairless has to do with the fact that they were founded by Asian populations, so they were pre-dispositioned genetically with hairlessness.
Kambiz
Kambiz
March 17, 2008 at 9:24 pm
Between 45ka and 30ka, the ancestors of the modern oriental people eg. Koreans, Tibetans, Vietnamese, and the Native Americans, and the Paleo-Siberians (excluding later mixtures) were geographically isolated at Lake Baikal, where they arrived during a warm inter-glacial period by following the flight path of migrating waterfowl from the African Rift and Paratethyan Black-Caspian basin.
They lived at the north end of Lake Baikal along plentiful brackish hot springs at the edge of the Amur tectonic plate, and they maintained a habit of daily bathing and foraging (fish, molluscs, seaweed, reeds, lowland millet grains as well as medium size animals that came for water and salt) in the warm-cool waters there, continuously through the ice age.
They did not have a strong stone tool culture, and probably used snares, traps, pits, weirs. Their huts were probably 1/2 dug into the ground, covered with skins and bark, insulated with reeds including tatami-like mats and furs.
35ka, tectonic shifting opened the Angara river (the only outlet of Lake Baikal) which sent much of the warm water northward into the Yenesei river and the Arctic sea, but the springs still provided warm water locally.
This caused a major diaspora.
The tribe budded off into small expanding mobile bands venturing along connected river basins (Lena, Yana, Yenesei, Angara) and Arctic-Beringia coasts, having partially adapted culturally to colder water and climate with skin boats and improved big game hunting methods and switching from hot baths (retained in Japanese) to sweatlodge/sauna cleansing which depended on firewood fuel rather than hot springs. Because these bands were mobile, running out of fuel was not an issue, unlike sedentary people. Stone tools were made, but bone and ivory were as commonly used.
At the same time in the west, people had adapted biologically by growing longer body hair, they lived along the Medit./Black/Caspian sea and marshes on fish, waterfowl and game thirsting for water and salt, including migratory herds, and quarried for stone in the Caucasus, Alps etc.
After the last glacial maimum, warming induced some Baikal people to expand eastward along the Amur and up/down coasts to Korea/China/Japan (Yayoi), and others to migrate southward inland following flocks to Tibet, Burma and then south China.
So we end up with Lapp, Manchu and Eskimo Inuit people who are relatively hairless biologically well adapted for warm seashores but culturally adapted for tundra plains and arctic coasts; and blonde hairy Norwegians and swarthy Georgians biologically adapted for sub-tropical forests and deltas but culturally adapted for plains and mountain valley herding and fjord fishing in open plank boats.
A bit brief, but that’s the meat of the matter.
DDeden
March 18, 2008 at 12:18 am
Truly ‘hair raising’! What is more intriguing is the evolutionary perspective of ‘intertriginous hairs’.
Amiya Sarkar
March 23, 2008 at 6:25 am
That’s due to hydrodynamics as a selective agent, (barring conflicts with nursing infants both on land and in water, thus the lack of beard and chest hair in adult females). Better hydrodynamics = less macroturbulence = better oxygen and energy conservation. So, as you state in your post, “friction” reduction, especially in dense, viscous seawater during daily diving for seafood. Since children were not primary foragers, there was no strong selective pressure for better hydrodynamics until breeding age, so aside from scalp hair, children have only vellus hair and tend to be less ‘curvy’ compared to adults. Adult body form is more curved, partly due to childbirth requirements, so the crevices contain fluffy hair, what Darwin termed ‘coarse’ hair, while the scalp and body hair may be straight, wavy, curly or nappy).
Coarse hair is nearly the same in all ethnic races, while the other body/mustache/scalp hair is unique to each group. Why? Because coarse hair is most effective in changing water flow from energy-costing macroturbulence to low friction microturbulence. Great apes lack an under-fur found in lesser apes and monkeys.
Coarse hair at joints/crevices, subcutaneous fat at other locales, the head hair having unique requirements (infant grasping, nursing, previous hominoid hair position, lice being factors).
IMO but not certain, this coarse hair in humans is the remainder of the primate under-fur, which was retained for better swimming and diving, but lost in the apes (which never dove).
DDeden
March 27, 2008 at 1:21 pm
This all makes my think of a totaly different mater. Why does it looks like their was only a limmited amout of admixture between cro-magnon and neandertals. I think because neandertals evolved in a temperate to ice-age climate in the northern hemisphere seperate from other human groups since more than 1 million years (dmanisi ?)and thus had thick pelts (no need to ware clothing) making them sexually unattractive to hairless humans. This does not make them less human, only different.
Since we know that neandertals lived as far east as Siberia, it is only waiting untill an ice-mummy neanderthal is found in the permafrost .
adriaan
March 28, 2008 at 11:03 am
Adriaan, that’s an interesting idea. Both polar bears and mammoths had fluffy fur pelts and abundant skin fat. I figure Neandertals had lots of skin fat, but I’m not sure about the pelts.
My thoughts on neandertals: During the warmer periods they were probably naked, they probably swam a lot, they probably were quite hairy, maybe they had reddish -brown woolly body hair. Perhaps they group-ambushed various prey at waterside, then removed the whole pelt (say of a bear or moose) from the carcass, then smoked it, melting off any attached fat, killing the lice etc. then simply wearing that as a longsleeved outer garment during the cold months and adding some squirrel pelt mitts and grass-filled boots with twined cordgrass or tendons to keep everything tight and warm. Later simple sewing gave a better fit, cro-magnons may have brought sewing improvements to the area.
DDeden
March 30, 2008 at 10:26 pm
whoaaaaaa you have a lot of hair
jdfkjsdnfjndskf
March 31, 2008 at 9:54 am
I think a group of early hominids, who we mistook to be ‘barbarians’ were in true fact ‘barberians’, went around kidnapping hairy people and with really lousy scissors gave them bad haircuts so women ran away, preventing them from having babies. With hairless people having a strong sexual selection advantage, barberians began to lose their natural prey and their numbers diminished sharply – which in turn explains why it’s so hard today to find a good barber, especially for under $20.00.
Justin Geste
April 16, 2008 at 10:48 am
I’m way late in this discussion, but I’m curious about two things:
1. Why most hairy men seem to have chest hair but not necessarily hairy backs. Great apes don’t have chest hair but they have hair on other parts of their torso. I know chest hair is related to levels of testosterone, even though that doesn’t guarantee a man will have chest hair, he probably won’t have a hairy chest without enough of it. So why chest hair and not back hair? Maybe so a baby can cling to his chest? Or maybe the sun on his back caused him to overheat and so losing it was an advantage.
2. It seems like a lot of arguments for chest hair have to do with living in cold climates. But do chest hairs really make a man that much warmer? It doesn’t seem like it would.
Jason P
September 27, 2008 at 2:41 pm
I would think if it evolved because men needed it then women would need it too. No?
Cathleen
October 18, 2011 at 6:31 pm
No cold climate mammals have body hair patterns like humans, but the walrus has a similar sparse distribution of hairs, not for warmth but for crevice filling, turbulence reduction and waterflow sensation during diving, the same reason humans retained it. The chest is bumpy, so hair fills in the low spots, the back is less bumpy except the tailbone-buttocks area which has some hair for better flow in water.
The sirenians (manatee/dugong) have a similar pattern of sparse hair. Dolphins swim so fast that waterflow turbulence is not reduced by sparse hair, so they lost all their hair. Walruses, manatees, humans swim and dive slow, sparse hair reduces their drag. Women have less body hair because they spent less time diving and more time wading in the warm shallows with the kids and beachcombing.
DDeden
October 12, 2008 at 2:11 am
I have heard about high histamine ( Histadelics ) Have lower body hair .
While people with low histamine ( Histapenics )
Have increased body hair.
Now histamine helps stimulate the immune system.
Northern eurpopeans / Northern asians generally have far less body hair than their related southern populations .
( Italians vs Nordics ) (Asian indians vs Chinese)
It is possible that the higher histamine may be helpful to ward off disease in the northern lands ( Although it seems most disease are far more southern in orgins )
Also Histamine increases blood flow , circulation , lowers blood pressure.
It is possible that the higher histamine levels could help northern populations withstand the cooler climates .
( Only problem ) I tend to find almost no data on histamine in ethnic groups . ( The few i have tend to have said african americans have higher histamine )
Which i find strange . . Histamine lowers body hair ( Asians , Northern Europeans ) Check
Histamine lowers blood pressure ( Asians , Northern europeans ) Check
Histamine causes obsessive compulsive disorder .( In my opinions , Asians and Northern Europeans have much more obsessive compulsive tendencies than african / southern groups )
But african americans have more asthma , allergies . ( So that is the true definition of the general traits of histamine )
But there are also multiple histamine receptors and distributions through out the body!
So perhaps asians , and whites have a alteration of histamine that influences a different end of the histamine traits .
I also tend to find almost no data on histamine levels in humans vs apes or other animals .
What i have found is .
Vitamin C defiency causes Exessive Histamine . (Vitamin C is a anti-histamine )
Also Humans are one of the few mammals which can not create our own vitamin c ..
The mammals inclue ( Apes , Guniea pigs , Fruit eating bats , Humans )
All eat alot more fruits containing alot more vitamin c than humans .
So perhaps a Vitamin C defiency has caused ( Humans to lose their hair , Through Exessive Histamine .
( northern populations would have had far less intakes than vitamin c . ( Matches the less body hair in northern populations )
Which also includes the ( Mayans vs the northern plains – eskimo indians )
The mayans are more hairy .
This seems to be a general world wide trait vs ( Northern Vs Southerns )
The only exeption seems to be the ( Hairy ainu of northern japan )
Which does not truely count!
For the ainu are thought to be a tibetian / nepalese transplant into japan ( 6 thousand ? years ago ? or so)
Best evidence of all is the sea mammals .
Sea mammals lack hair . ( They also lack vitamin c!) = Less vitamin c = More histamine = Less body hair .
Nothing in the sea really makes vitamin c . So all sea mammals have almost no existant vitamin c!
It is thought that vitamin c is needed to protect life on the surface ( Not in the seas )
Thus it is interesting that Sea Mammals + Humans are the only ones on earth to not have fur!
Since humans can not make Vitamin C out of carbohydrates ( Like most animals can ) Since we do not eat tons of fruits each day like a monkey!
It is thought we would need to obtain 1 gram of vitamin c a day to saturate our blood with vitamin c ( Like animals which create their own vitamin c make )
This theory explains why Sea Mammals have no fur . Explains why humans lack it . It also explains why the northern populations which lack Fruits in their diets also have less body hair .
The Testosteronee Theory is not true . ( African americans have higher testosterone than whites ) Yet generally have less body hair .
With this said . It is in my personal opinion . That humans began to first lose their fur from a vitamin c defiency . Than later on this was reinforced by natural selection which rewired us to perfer less fur .
Thus we became furless .
Matt
December 19, 2008 at 3:39 pm
Sorry Matt, you’ve got so many errors I can’t correct them all. Seaweeds have vitamin C, all anthropoids lost the ability to produce vitamin C including foliavorous monkeys (including the swimming proboscis monkey of Borneo mangrove swamps), many sea mammals have abundant fur and/or vitamin C in their skin, etc.
DDeden
January 12, 2009 at 7:20 pm
Another thesis
Because God wanted us to be this way you overscientifying it ;)
devoter
July 24, 2009 at 3:25 am
Wrong.
Kambiz
July 26, 2009 at 7:19 am
And with this comment you will close the discussion!
This argument eases the mind who desnt like to make hard questions, and keep us in ignorance.
Again!
Antonio Xeira
September 11, 2011 at 1:53 pm
KAMBIZ, I love your opinionated-ness.
Devoter: Finding answers about life is part of being an open-minded person. Why would you choose to live ignorantly when an answer is out there? Besides “God wanted us to be this way” or “it was meant it to be, because of God”. Do you think God’s plan was to have his sons and daughters murder and be cruel people just to go to Hell? You think He created them just for that? If not, then how can you possibly believe we were just meant to be hairless because God wanted us that way?
STOP YOUR IGNORANCE.
Food for thought..
KelsAM
January 19, 2010 at 8:59 pm
There are probably a multitude of evolutionary reasons why we grew to have less hair.
I’d imagine that the primary reason was that we became able to insulate ourselves and thus its evolutionary importance was lost.
Assume men are hairier due to spending longer periods working/hunting outdoors, than women so some residual benefit still remained
.
steve
September 11, 2011 at 2:06 pm
Persistance hunting by the oldest tribe on the planet – San Khoisan people.
This is done by hairless men walking and running for many miles tracking a prey animal in midday until it collapses with heat stroke. Humans have built in advantages – sweat glands for cooling and more efficient bipedal long distance locomotion.
Mark
June 15, 2010 at 9:26 am
I’m afraid I’ll have to tip my hat in with DDeden here. There is some compelling evidence suggesting that many of our “peculiar” and unique traits are adaptations for living in a shoreline habitat. Many of our relatives take a bipedal stance when wading in shallow waters while crossing or foraging, and while hairlessness isn’t a hard rule where water is concerned, it certainly helps to eliminate drag (not to mention, just imagine trying to muck through the mud with all that hair!).
If that’s not suggestive enough, consider that we humans require extensive amounts of EFAs in our diet (particular to note here – DHA) to support our massively oversized brains. EFAs are essential fatty acids that are called “essential” because the body cannot synthesize it and requires it. We can thank a diet of abundant EFAs for the resources needed to evolve the brain size that we have today. There are very few sources of EFAs. There are a few plant seed sources of some EFAs, such as flax, hemp, borage, etc, but these do not contain the needed DHA – the most abundant source of this oil is in seafood, such as fish and shellfish. The same can be said for Glucosamine and Chondroitin, which support our joints, and is also primarily found in seafood.
Anyway, my two cent’s worth.
Dana
June 28, 2010 at 12:23 pm
Thank you Mark! There are books on this subject: Why We Run (by Bernd Heinrich, PhD animal physiologist and ultramarathoner) and the recent bestseller Born to Run by Christopher McDougall (another ultramarathoner).
Basically, they’re right in that we don’t know why hominins INITIALLY went bipedal, but the genus Homo, according to the evidence, became the best long-distance hunter on the planet long before we invented anything more complex than a hand axe.
Because our bipedality gives us an extremely efficient (if slow) running gait that a trained human can keep up for four hours, and because our relative hairlessness lets us dump waste heat easily, our ancestors hunted by running animals into heat stroke, then killing them by bonking them on the head with a rock. No fancy tools, just persistence.
While I agree with the anthropologists that hairlessness may have started for some other reason, the massive selective advantage it gave our ancestors (being able to eat meat if you can jog for four hours) was a powerful selective pressure. Couple hairlessness with our form of bipedality, and we become highly effective omnivores.
The aquatic ape hypothesis is seductive, but it suffers from testability. Your average dog can swim faster and hold it’s breath longer than your average human, yet no one hypothesizes that dogs evolved from recent aquatic ancestors.
heteromeles
July 5, 2010 at 6:06 am
But weren’t the dudes the hunters? Shouldn’t, by that theory, women have more hairiness, not less, then men? So far, I have to think it has to do with being in water.
Cathleen
October 18, 2011 at 6:36 pm
but why do we still have hair on our heads? and what about people who go bald? does that mean anything significant
recconoatored
July 28, 2010 at 4:10 am
Is it even possible to know the full evolutionary when and why of how we got to be the way we are?
I think that risky lives and small populations of a smart critter like a proto-human could see clever but maladapted individuals surviving to become, as much by chance as fitness, the foundation mums and dads of homo sapiens. ie we are like we are by dumb luck because once upon a time all the fittest men didn’t return from a hunt and the ugly sod with no fur, ordered to stay behind and do menial work – the one who hung animal skins around himself just to keep from freezing – goes on to father some clever furless kids who hung animal skins around themselves too.
Maybe not literally but the how and why could rest on pivotal events in our ancestral history like that.
I’m not convinced that sexual selection would be all that selective amongst very small groups of proto humans either, at least until well past the events that brought on the the demise of the furred. Like I do with choosing to surmise a male as the founder of the line – just to be contrary – I’m surmising the habit of collecting furs and fill their shelters meant when a nasty cold period hit the region it wasn’t the naturally furred ones, but the furless who did best.
Ken Fabos
August 5, 2010 at 9:19 pm
Sorry, after consideration, I think sexual selection within very small groups of proto-humans would indeed have to be an important factor, however I doubt that a fur-less mutant would be the most attractive even if, by cleverness, skills and parental social standing they could still be desirable as a mate. I suspect that, initially at least such an appearance would be considered more reminiscent of babies than of juveniles on the verge of sexual maturity; I am presuming that juveniles would have been furry like adults prior to changes that made us fur-less.
It might take time and the right situation for furlessness to reveal itself to have advantages with respect to shedding excess heat – and be dependent on other adaptations like more and more watery perspiration that would not have happened at the same time. Advantage from reduced parasite load would at least be fairly immediate – my own hypothesis that finer, sparser hair allows greater tactile sensitivity to very small impulses than thick fur would make for better awareness of parasite presence as well as allowing them to be more visible for removal.
Ken Fabos
August 12, 2010 at 5:56 pm
I can’t read all those comments, but I think that the reason for fur loss might happened because of the human brains evolving and starting to make clothes when they were cold. And because of the body fat.
But for bold people.. That just might be a genetic disorder.
I’m not really an expert, and I’m not old enough to be one, but that’s just an idea.
Jelena
September 26, 2010 at 1:23 am
Hi there
V.interesting comments, great to see the theories and love of knowledge here…
I have a question which I don’t think has been covered above, apologies if so… My 6 year old just asked why I have a hairy chest and he doesn’t. I tried with some “don’t worry son you’ll get one too” support but that doesn’t seem to be his interest ;)
He asked if it’s because mums and kids stay at home where it’s warm whilst dads go out in the cold. Sounds basic but not a bad theory for a young mind ;) Or if it’s just colder when you’re taller… (our previous question was why there is snow on a mountain even though it’s closer to the sun, so I think he’s seeing if any of that can be applied here… (that one was difficult to answer!)
Any thoughts on this specific difference of why dad has a hairy chest and not the little ‘un?
Cheers all, and keep questioning :)
Dan
Dan
October 24, 2010 at 2:17 pm
Testosterone my friend. It causes hair growth on the body but surprisingly inhibits hair growth on the head.
Kambiz Kamrani
October 26, 2010 at 3:32 am
Hi Kambiz,
Thanks for the reply, but this is not quite the question I wanted answering ;)
For me, testosterone would explain the “how”, but not the “why”…
Body: Dude, you need hair when you get to 13, so I’m going to give you it using some different levels of this n that
Me: No worries sounds good, but why?
Body: Dunno, I just work here innit
I mean, monkeys have hair when they are babies right?
Big disclaimer: I failed Biology ;)
Dan
October 26, 2010 at 7:30 am
Monkeys have both an under-fur layer and outer “guard hair” fur layer, this is the basic ancestral trait for all mammals (fur + milk nursing = mammal).
Great Apes have lost the inner fur layer due to tree-top nesting in tropical rainforests, where thermal insulation was less significant, but biting insects weren’t (so some apes have thick fur on their more-exposed back but less on their chests (they sleep curled in a ball in the bowl-nest)).
Humans, on the other hand, split from the apes 5,000,000 years ago, with the chromosome #2 translocation, which in my opinion induced altered behavior, by producing a hominin species which spent more time at waterside foraging & bathing and sleeping in inverted bowl-nests on the ground, aka geodesic dome-like huts, waterproof and insect-proof. Thus no selection for fur coat.
DDeden
sayang
October 22, 2011 at 11:24 am
Just a thought, but what about fire? When humans “discovered fire”, I’m sure having hand and arm hair didn’t feel too good when singed.
MattR
June 28, 2011 at 7:14 pm
The most recent view is the naked love theory. Here’s the theory’s abstract:
All primates except human beings have thick coats of body hair. This suggests the primate ancestors of human beings likewise had such body hair and that, for some evolutionary reason, lost their body hair. Various theories have been put forward but none is fully adequate. This article presents the “naked love theory.” This theory locates the origin of human hairlessness in the ancestral mother—infant relationship. In this view, hairlessness is ultimately the adaptive consequence of bipedalism. Because of bipedalism, ancestral infants lost their prehensile feet and thus lost the ability to grasp the mother’s fur with their feet, as do other primate infants. Early bipedal mothers were thus under pressure to carry the infant. Therefore infants survived only if mothers had a strong desire to hold them. Because of the pleasure of skin-to-skin contact, the desire to hold the infant would have been stronger in mothers possessing a hairless mutation that enabled them to give birth to hairless infants. Survival of these infants would have then been greater than that of hair-covered infants. The hairlessness that began to appear in this context of maternal selection was then reinforced by sexual selection in the male—female sexual relationship. This is because a hairless sexual partner would have enabled the hairless individual to recreate the pleasure of skin-to-skin contact in the mother—infant relationship. This theory then helps to explain the evolutionary origins of romantic love.
Wil
August 28, 2011 at 3:25 pm
I wrote quite a bit about how ancestral daily semi-aquatic foraging may have produced the mostly hairless condition in humans. There is one additional factor involved, more significant in general hair loss than aquatic foraging. Guess it!
DDeden
September 2, 2011 at 11:12 am
The aquatic theory…. you see that aquatic mammals have more fat and, having humans more underskin fat than other mammals, you think we had an aquatic time in our evolution.
I think we swap cause and effect: water itself doesn’t cause fat growth. The heat transmission in water, the heat you lose, cause you to grow underskin fat.
The lowering of body temperature causes, through selection, a favour for underskin fat.
Now we have hominins without fur; hominins that suffer the cold temperature during the night. They use fire but who camped knows that fire is not always so effective.
So…what is the second choice of a mammal to protect is body against cold temperature after he has lost is fur? underskin fat, also in air environment. It is not water, it is temperature loss that causes underskin fat, don’t you think so?
Do human groups living in artic regions since thousands of years have a higher average level of underkin fat in comparison with tropical humans? This could be a good indication.
Alessandro
October 24, 2011 at 2:03 pm