The evolution of human hairlessness and skin colour

24


Discussion by: StickyWillie

I've been interested in human evolution for many years but have yet to find any coherent information on the the two subjects above.

The first question is, of course, why, when evolving in a diverse continent where evolution chose to keep our fellow primates and particularly our close relatives the apes hairy, did we lose our hair? Hair doesn't preserve or fossilise well over millenia so there are no clues in the record as to when or why this change began or how many millenia it took to completion, bearing in mind that some of us males are still hairy enough for the change to be considered less than complete on a pan-species basis. So, I'd be interested to know if there's any accepted wisdom on the subject.

Secondly, skin colour is something that facinates us, some us for entirely the wrong reasons. Now, I realise that having divested ourselves of hair at some point, skin colour changes from the dark colour amenable to a tropical climate could be stimulated by humans moving out of Africa into climate zones where sunlight was less of an issue and heat retention became a little bit more important. But how long did this take? Is there some information say, in the genome, perhaps some spoor in the mitochondrial dna for instance, that could put a timescale on this? Also, did it happen more than once or simultaneously as different and disparate small groups of our species spread thinly across the European and Asian land masses? And would paler skins revert to darker skins as groups moved into hotter climates. In other words, are we, from a species point of view, flexibly photosensitive from a skin colour point of view?

And finally, I do hope that everybody understands, considering the sensitivity surrounding skin colour, that I am asking this only out of curiosity.

24 COMMENTS

  1. would paler skins revert to darker skins? … In other words, are we flexibly photosensitive from a skin colour point of view

    Now that’s an interesting question. Is there any way to trace the pigmentation of our ancestors? Certainly it seems plausible that pigment changes as a response to environment can go either way, and back. As I understand it, the pigment is the result of a balance between protection from sunburn vs the need for solar-powered vitamin D synthesis. Vitamin D deficiency impairs dark skinned people in high latitudes with cloudy skies, while sunstroke impairs pale skinned folk in the tropics and deserts. I’ve long understood that white folk are just black folk who’ve been too long under a cloud, but I hadn’t thought of some dark folk being pale ones who went back to the sunshine.

    On hairlessness, there are as I understand it several competing theories. Or suggestions, speculations. I don’t know if there is enough evidence to call any of them a “theory”. Hypothesis maybe. The most entertaining of which (IMHO) is the Aquatic Ape Hypothesis. I said “entertaining” on purpose. I don’t know if it is more “likely” or “plausible” than other theories. It’s not popular among anthropologists, though it hasn’t been refuted (last time I read about it). It has been discussed here from time to time. No references, it’s not that hard to Google.

  2. Variation in skin colour may just be an inevitable consequence of diminishing hairiness.

    With body hair there’s some speculative advantages that might have enabled selection pressure to drive evolutionary change towards hairlessness. They’re mostly to do with lifestyle rather than sexual selection.

    Sexual selection may play a role in human hairlessness. It is possible that stealing the fur off other animals and then wearing it is some kind of showing off, demonstrating hunting prowess. Possibly the origin of clothing, which came in handy after humans migrated away from tropical areas.

    Some possibly reasons for reduced hair:

    Thermoregulation: ease of sweating and evaporation as humans became long distance scavengers. Humans have the most endurance and range of any land animal. And regulation of body heat is important for very prolonged strenuous activity. Presumably this evolved in tropical environments where it is hot all the time, rather than humans evolving seasonal shedding behaviour similar to my Labrador dog.
    Parasites are easier to see and deal with in the absence of thick fur. (With the retention of head hair to enable primate grooming.)
    Finer and smaller hairs are more sensitive for signalling parasite attacks or the presence of venomous spiders and ticks, or mosquitoes.

    Adoption of clothing: hairlessness may be more compatible with clothing.

    Enhanced UV reception with more surface area on which to manufacture vitamin D from sun exposure during weak sunlight. Perhaps associated with long northern winters or a long period of no summer caused by asteroids or volcanoes.

    Finer and smaller hairs are more sensitive to wind direction. The diminishing sense of smell in humans implies the need for another mechanism to maintain awareness of wind direction. (Smell not being important for humans to locate prey, but still important for prey to evade humans.)

    I don’t think the aquatic ape idea explains human hairlessness because seals, otters, and platypus are usually hairy. There doesn’t seem to be any relevance to being hairy or not for shore-dwelling sea mammals, which seem to all be hairy. On the other hand all land mammals capable of extraordinary range and endurance are hairless – unfortunately humans being the only example. It is possible that the long-range, high speed, scavenging lifestyle is only available to cooperative, intelligent, bipedal apes. So you’d need other species of humans to compare against.

    I think that it’s interesting that hair in humans is retained in some areas rather than others: head and jaw area (in men), and sometimes forearms, back, and upper chest. These all tend to be areas where subcutaneous or deeper abdominal adipose tissue doesn’t normally accumulate. Adipose tissue being an insulator. So it would make sense that some degree of hairiness be retained in areas that don’t tend to get as well insulated in cold times, which typically follow times of growth and excess feeding.

    • In reply to #2 by Pete H:

      …Some possibly reasons for reduced hair:
      Thermoregulation: ease of sweating and evaporation as humans became long distance scavengers. Humans have the most endurance and range of any land animal.

      Whilst we can’t be absolutely sure, this is one of the leading candidates. Life on the savannah was very different from the forests. Not only the lack of cover but also the predatory competition made it difficult to find food, and humans began to exploit the niche of hunting during the hottest parts of the day, when most animals tried to keep cool.

      The main strategy seems to have been endurance running and evidence for that is in our bodies. The gluteous maximus (our backsides) seem to be connected with running rather than walking – they really come into their own with distance running. We also developed waists, so that our pelvises could rotate in opposition to our upper bodies (just as happens when we run). And we (uniquely – other apes don’t have this) developed the small nuchal ligament that attaches to the back of our skulls and prevents our heads jerking forward when we run.

      But most of all, we began to sweat a lot, to cool down in the midday sun. We have more sweat glands by far than other apes. Part of this process involved losing most of our fur (well, not quite – most of us our still covered in very fine hair, but we lost the thick stuff).

      With all these modifications we could run down any animal on the savannah.

      Of course, none of this was planned (natural selection was responsible) but later sexual selection may have played a big part, but by then we’d been naked apes for a very long time.

      • You’re probably right about sweating.

        Absence of fur would make a big difference to the rate of evaporation and the location of evaporation providing maximum temperature drop at the skin surface. The other approach, taken by most other furry mammalian predators, is to stop and take a nap frequently to allow the body to cool off and recover. But that gives most prey an opportunity to escape. Prey species are either very large and difficult for predators to attack, or quite small and slender and so more efficient at getting away. They only have to be slightly more efficient than the predators. But they’d have to be extremely efficient to get away from human predators.

        So a relatively sudden mutation, like hair loss (which might be a very quick mutation compared to the acquisition of extra hairiness), that enabled our extraordinary human endurance may have resulted in a massive advantage for humans over all other predators and prey.

        Other things like the use of clothing and parasites would be secondary effects. Same for skin colour – only relevant after the fur has gone. (I think I read somewhere that chimpanzees are light skinned under their fur. Only the exposed parts like noses and ears etc. are dark.) And sensing the wind direction can be quite salient by rotating the body slightly when one’s body is sweat covered. Same thing when licking the lips and facing into the wind: this makes it easy to test wind strength and direction by feeling how fast the lips dry out and cool down. No real need for whiskers or other hairs on humans.

        In reply to #3 by Pabmusic:

        In reply to #2 by Pete H:

        …Some possibly reasons for reduced hair:
        Thermoregulation: ease of sweating and evaporation as humans became long distance scavengers. Humans have the most endurance and range of any land animal.

        Whilst we can’t be absolutely sure, this is one of the leading candidates….

    • In reply to #2 by Pete H:

      On the other hand all land mammals capable of extraordinary range and endurance are hairless – unfortunately humans being the only example

      I do hope that was meant to be a joke. Anyway, best laugh I’ve had today.

      Apart from that, thanks for outlining what I understand are the mainstream speculations on how hairlessness evolved. One other part I found entertaining in a cart-before-the-horse kind of way was the notion that our ancestors lost their own hair subsequent to adopting the practice of wearing other animal’s furs as hunting trophies. Nice piece of convoluted thinking (IMHO). Head hair would then be explained by claiming that hats were rarely fashionable.

      …With the retention of head hair to enable primate grooming

      To my untrained eye this looks like another odd kind of inversion. Total baldies had less breeding success, judging by results, but the head hair/grooming connection seems very speculative.

      it would make sense that some degree of hairiness be retained in areas that don’t tend to get as well insulated

      That seems more plausible. Still, it’s all very speculative.

      • If you’re interested in speculative connections between human head hair and primate grooming then check out the phenomena now generally known as ASMR. Easily found on YouTube where many people now compete to generate an intense ASMR response in viewers. You’ll find that hair-related topics are a significant common trigger. Though, unless you’re an ASMR responder, you’ll probably assume this stuff is ridiculous nonsense.

        Essentially it’s believed to be a complex nervous system response that causes intensely odd and pleasant sensations in some sensitive people. It might be a remnant function that once (and possibly still) played an important role in primate tribe socialisation. It might also be a little like what pets experience when their fur is stoked. I suspect ASMR might play a role in triggering significant placebo responses in various pseudoscientific medical treatments like acupuncture and an entire range of quack therapies ranging from tarot card readings to iridology.

        A problem in many areas of social science is that there are often flawed assumptions of uniformity and randomness in the population under investigation. Things like placebo effects are very unlikely to be uniform across any sample population. This affects some areas of biology, especially nutrition and public health, and some areas of economics where a very high proportion of statistical inference-based published and peer-reviewed research is believed to be irreproducible (or even worse: reproducible but still false anyway). ASMR may be very significant in human interaction, but it seems to only affect some people some of the time. So it’s slipped under the radar and is probably doomed to remain indefinitely speculative.

        It’s possible that reduced body hair is too easily explained (thermo-regulation). And retention of some hairs as a wick for pheromones is also obvious. What is much more difficult and interesting to explain is the retention of head hair. ASMR might be the key.

        In reply to #15 by OHooligan:

        In reply to #2 by Pete H:

        On the other hand all land mammals capable of extraordinary range and endurance are hairless – unfortunately humans being the only example

        I do hope that was meant to be a joke. Anyway, best laugh I’ve had today.

        Apart from that, thanks for outlining what I understand ar…

        • In reply to #16 by Pete H:

          Thanks Pete. Interesting topic. I’m learning new stuff, which is great. I enjoy the speculation, as long as it isn’t too daft, but I’m also happy to see speculative sandcastles washed away by the rising tide of confirmed knowledge. Many speculations I expect will fail as more solid data comes in from DNA research.

  3. Sweating, that’s how we lower our temperature, and sweating arguably came about when we moved on to the Savannah and started hunting and migrating. Mammals usually pant rather than sweat to regulate their temperature, but we somewhat evolved differently.

    Melanin and other compounds I believe protects from UV, and darken the skin. It’s not the really to do with the tanning process. There’s nothing sensitive about skin colour, or shouldn’t be anyway. It’s just how your ancestry evolved a way to survive in hot dry climates.

    • In reply to #5 by obzen:

      Sweating, that’s how we lower our temperature, and sweating arguably came about when we moved on to the Savannah and started hunting and migrating. Mammals usually pant rather than sweat to regulate their temperature, but we somewhat evolved differently.

      Melanin and other compounds I believe protects from UV, and darken the skin.

      yes

      It’s not the really to do with the tanning process.

      what? Isn’t tanning an increase in skin melanin to give short term protection from UV?

      There’s nothing sensitive about skin colour, or shouldn’t be anyway. It’s just how your ancestry evolved a way to survive in hot dry climates.

      actually my ancestry evolved a way to to survive in cold, wet, cloudy low UV climates. West Europeans are the strange humans that almost completely eliminated skin melanin

  4. I think there is some significance in the fact that the nerves that deliver pleasurable sensations are the recently discovered c-tactile nerves which only terminate on hairy skin. The shrinkage of hair length over the bulk of the body may have been driven by temperature regulation or other requirements but it is possible that there was a related reduction in pleasurable skin sensitivity.

    Long hair can act as a mechanical collector and amplifier of “touch” being a tangle of levers relaying a small finger movement, say, efficiently to a large area of c-tactile nerve endings. (Touch the hair on the back of your head lightly with a finger.)

    Without this tangle of levers the small hairs on “bare” skin must be rubbed at a speed of about 4 to 5cm/s to gain the maximum pleasurable effect. This “optimum speed” for maximum pleasure may be to coopt the triggering of enough nerves within the 20 millisecond time frame (or whatever) to be taken as coincident and therefore a single event. (Aside: Coincidence of stimuli is a crucial mechanism the brain uses to relate one stimulus to the other or to many. A certain time tolerance is allowed for what is deemed coincident, but is quite sharp in its boundary. Stand in a field with an assistant 100m away and watch his lips through good binoculars as he shouts at you. Voice and lips are out of synch. Have him move closer and repeat. At some point synching suddenly appears perfect. A few steps back its out, a few steps forward its perfect.)

    Head hair is different from body hair and may have additional drivers and mechanisms for its retention (male pattern baldness may hint at this, so too its fineness like grown out baby hair) but pubic hair’s location may hint at its tactile function and an extension of the grooming function with reproductive repercussions. Body hair’s role in pheromone dispersal shouldn’t be ignored either.

  5. Hairlessness might be:

    • more efficient cooling. Man was a marathon exhaustion predator
    • some period of our existence on a sea shore. Marine mammals are hairless. Elaine Morgan’s theory.
    • discouraging lice
    • we did not need hair. We had furs/clothing that could be adjusted as needed.
    • it is a side effect of neoteny

    Some years ago I read a paper about the speed of evolution of melanin to optimal levels for a given latitude. IIRC it was extremely rapid, only about 500 years.

    Darker has the advantage of blocking damaging UV rays. Lighter has the advantage of letting through enough UV to manufacture vitamin D. It is an optimal balance. I had a black friend who worked above the arctic circle. He was quite a novelty. He was the only black person in the Canadian north. I suspect humans may self select for an appropriate latitude. I have noticed black friends visiting complained about the cold. I thought it was fairly warm. (My ancestors came from the cold damp climate in Scotland and Northern England) So there may be other adaptations for temperature besides melanin.

  6. I am but a student, but I am in the midst of my anatomy and physiology class. I believe that the developmental defects suffered from lack of sunlight are very serious. Because people would be affected before the reproductive age, there would be a very strong pressure for light skin.

    As for hair loss, geneticists have a strong suspicion that the evidence is locked in the DNA of the two kinds of lice that affect humans; head lice and those little beasties that inhabit the nether region. So we know when that happened, and the reason is simple. Humans have a much higher count of eccrine sweat glands than our ape cousins. Sweating is essential to cool the body while on a marathon hunt, running down large heard animals. In high temperatures, humans can run for long distances and press other harrier animals to exhaustion and heat stroke because we do not rely on panting to cool, but our little eccrine glands.

    • In reply to #9 by zengardener:

      I am but a student, but I am in the midst of my anatomy and physiology class. I believe that the developmental defects suffered from lack of sunlight are very serious. Because people would be affected before the reproductive age, there would be a very strong pressure for light skin.

      As for hair los…

      Fascinating. Wouldn’t the intensity of the sun have a lot to do with it as well though? My understanding is that light colors reflect heat where as dark absorbs it and also light skin is more susceptible to burning so the environment (e.g. Africa vs. Europe) would also play a big role I would think.

  7. Couple of ideas I don’t see here, sexual-selection and aquatic-ape.

    Sexual selection is a proper scientific theory, but the other is not. Sexual selection would say hairlessness is like a peacocks feathers. It may have attracted mates by showing other anatomical virtues such as muscle tone and bilateral-symmetry (bitches love bilateral-symmetry). Aquatic Ape is a neat little story explaining human’s affinity with water (swimming babies), fat distribution, hairlessness, and many other things about our species. It’s not scientific at all, just a cool story. It might be true, but there’s no scientific evidence. The logic is faulty… but it could be true. Last I heard it was still unfalsifiable.

    In other words, are we, from a species point of view, flexibly photosensitive from a skin colour point of view?

    That sounds a bit Lamarkian. It would not be photosensitivity, in that photons would not be driving the variation. Even in a single family of narrow ancestry, skin color can vary greatly, within a certain range. This diversity allows for dramatic changes to occur in a short amount of time. If the very darkest or lightest 20% of a population experience lower reproduction, that can bring about a lot of change. I wonder about political-selection, as a driving force. India and Japan (Ainu) strike me as examples where skin color has been altered for social reasons, the result of memes.

    edit: ah, i see O’hooligan mentioned Aquatic Ape. And if you do google Aquatic Ape, be prepared for some nutty advocates. The idea became a Marxist-Feminist icon.

    • In reply to #11 by This Is Not A Meme:

      Couple of ideas I don’t see here, sexual-selection and aquatic-ape.

      Sexual selection is a proper scientific theory, but the other is not. Sexual selection would say hairlessness is like a peacocks feathers. It may have attracted mates by showing other anatomical virtues such as muscle tone and bila…

      there is a bit of significatn evidence for the aquatic ape theory, primarily what is called the “great human beach party” it was a point in time where our older ape ancestors actually migrated to the western coast of africa and spent a few generations along the beeches collecting moslty shellfish to eat as primary meat source. But once again no fossil hairs. Further genetic analysis may confirm this theory or disprove it. using the genes for hairryness to asses its evolutionary origin however it is the most parsimonious because it simply uses the same paralel for every other hairless mamal.

      • In reply to #12 by BenCarollo:

        In reply to #11 by This Is Not A Meme:
        no fossil hairs

        There is a big problem studying any animals that lived on the beaches. The oceans rise and fall even over a period of thousands of years. The stuff we want to study may be underwater where it is hard to study. I am hoping in the next century cheap robotic submersibles will become available to let us go exploring.

        There is discussion that where I live on the West Coast of Canada people lived right on the shore during the last ice age. The catch is all the evidence would be underwater.

      • In reply to #12 by BenCarollo:

        the “great human beach party”

        Thanks Ben, that’s another laugh for me. That’s a much better title than the Aquatic Ape Hypothesis. And while we’re musing on the goings on at the beach, check out this report on the [evolution of the penis] (http://www.scientificamerican.com/article.cfm?id=secrets-of-the-phallus).

        Put together, these suggest that our ancestors really were (beach) party animals. It’s a better Origin Myth than most, at any rate, not just because it hasn’t been refuted. Yet.

  8. read this on race and skin colour

    white skin evolved alongside humans moving north where vitamin D was harder to come by. This is why we see vitamin difficiancies in dark skinned people living in the north now.

    hairiness is a good way for mammals to regulate temperature. keeps you warm in the cold and protects from the suns heat. Interestingly enough, upright apes have retained their hairiness on top of their heads (ok not all of you), having evolved near the equator. Human body hair is different from head hair and there is evidence to suggest this is a later evolutionary addition after the thick monkey like hair receded. one example is the type of louse found in heads being a completely different species to those found downstairs.

    The equatic ape theory is interesting, not least because there are reports of humans who’s children cling to their mother’s hair while out pearl-diving. who doesn’t like a lady with nice thick, long hair? there’s a good reason for sexual selection to operate right there if you want your children to survive. As a young surfer I was told that “surfer’s ear” (see also swimmers ear; protective bone that closes up inside the ears of people who spend a lot of time in cold water)) is evidence of an equatic past

    I expect in truth though, these questions are a long way from being answered.

  9. Too late to edit, I see link formatting has gone awry. That’s not how it looked when I clicked submit.

    And a footnote: since the AAH seems to be burdened with feminist propaganda, I thought the penis link was appropriate for balance. It also segues nicely into the brain-vs-brawn competition, since humans didn’t go down the evolutionary route of some mammals where the biggest, strongest, toughest male is the dominant one that gets most mating opportunities, so pushing evolution towards bigger-stronger-tougher. With humans, if the penis link means anything, seems to be more like survival of the sneakiest.

    Explains a lot about modern humans, perhaps?

  10. All right, I thought of posting this as a new topic, but I think it fits here just fine.

    It’s pretty obvious that the loss of body hair most likely occurred gradually over a long period of time, with successive generations growing less and less hairy (as opposed to, say, a mutation that caused a hairless child to be born of hairy parents one day). And I have no trouble imaging how skin color could gradually lighten or darken over many generations due to slight mutations and variations.

    However, what about things like hair color and eye color? Are we assuming that these things changed gradually over time as well? Did hair color gradually change from, say, dark brown to blond over many generations with many intermediary colors? Or is it more likely that a random mutation caused a blond child to one day be born from parents with brown hair (or a blue-eyed child born from parents with brown eyes)? Are hair color and eye color controlled by single genes that could have been the result of specific mutations, or are they actually the result of many genes working together and therefore not likely to be the result of a single mutation?

    I’m assuming that these changes, like most adaptations, were gradual over time. But I have to admit it’s a lot easier to think of the intermediate stages from hairiness to hairlessness than it is to think of a gradual change from brown eyes to green eyes.

    Conversely, if these changes were likely the result of random mutation, why don’t we see this sort of mutation happening today? Are the cases of, say, a “pure” Asian child being born with blue or green eyes? Or a “pure” sub-Saharan African randomly being born with blond hair?

    I’m assuming, btw, that early hominids all had the same color eyes and hair color and that the variations we see today arose over time as humanity split up and were affected by the forces of natural selection in different ways. Perhaps this is an incorrect assumption, however. Is it possible that such variation existed right from the start and that there has always been random variations in hair and eye colors? If so, though, why do Europeans seem to be the only group that display this variation today?

    I’m sure I’ve made plenty of false assumptions in the preceding statements, and I welcome any and all corrections.

    • In reply to #20 by godzillatemple:

      All right, I thought of posting this as a new topic, but I think it fits here just fine.

      It’s pretty obvious that the loss of body hair most likely occurred gradually over a long period of time, with successive generations growing less and less hairy (as opposed to, say, a mutation that caused a ha…However, what about things like hair color and eye color? Are we assuming that these things changed gradually over time as well? Did hair color gradually change from, say, dark brown to blond over many generations with many intermediary colors? Or is it more likely that a random mutation caused a blond child to one day be born from parents with brown hair (or a blue-eyed child born from parents with brown eyes)? Are hair color and eye color controlled by single genes that could have been the result of specific mutations, or are they actually the result of many genes working together and therefore not likely to be the result of a single mutation?

      If, like me, you have blue eyes, you and I are both descended from the same ancestor who lived in the Caucasus region between 6 and 10 thousand years ago. It is a single gene mutation affecting the OCA2 gene. Source- Science Daily and a variety of google links, all very interesting stuff.

  11. Finding coherent explanations for “hairlessness” is difficult; scholarship on it has been poor in my opinion. It suffers greatly from having been singled out as an example of an evolutionary vestige that’s very uselessness has been cited over and over as evidence that evolution in humans has taken place. The problem is that it is based on failing to notice that body hairs (with their nerve rich follicles) are not useless, they are fully functional sensory organs that, amongst other things, are useful in reducing our exposure to parasites that can be vectors of serious disease.

    The ‘functionless’ and ‘vestigial’ labels have been very unfortunate and I think helped propagate the false idea of an ongoing evolutionary trend of ongoing loss of body hair; after all, if it serves no function it is likely to be lost entirely. Add in a modern, socially acquired dislike of body hair and we have “proof”! Except that it’s wrong; Pete H mentions the sensory function of hairs; that’s good because that’s been an ongoing peeve of mine. How can multiple scholars, over more than a century, fail to even notice that hairs have such a function? From Darwin to Jablonski that function is treated like it isn’t there at all; strange, given that I would argue it’s the most survival significant function of body hair in modern humans and that begs for explanation.

    Even calling humans ‘hairless’ or ‘naked’ or having ‘functional loss of hair’ is misleading. I suspect that is an error that dates back to Darwin (I’m blaming Darwin; it’s traditional!) -

    Darwin, in “Descent of Man” -
    “No-one supposes that the nakedness of the skin is any direct advantage to man; his body therefore cannot have been divested of hair through natural selection”. He went on to attribute ‘nakedness’ to sexual selection – ” whilst our female ancestors were gradually acquiring this new character of nudity, they must have transmitted it almost equally to their offspring of both sexes…”

    I’m supposing that Darwin was wrong.

    A couple of points that I think deserve consideration; human furlessness is most strongly expressed before puberty within juveniles and, no matter the dimorphic (male/female) differences emerging in adults, homo sapiens children all share this as a universal characteristic across the entire species. If it were a conssequence of sexual selection we should see wide variation of hairiness within the young as well as within adults. The disadvantages of furlessness are borne most of all by the young.

    Hominid evolution is qualitatively different to any other evolutionary line; clever tool users who are capable of behavioral adaptations to overcome physical limitations can tolerate traits that would otherwise be headed for extinction. Humans without fur can survive to be a viable variant despite the problems it brings; changed circumstances generations later can reveal advantages that may not be initially apparent, such as being less susceptible to some (parasite borne) diseases. Or show improved hot weather endurance in a changing climate. There doesn’t need to be an immediate advantage; the furless form might have struggled to survive at all, but the means used to overcome their disadvantage – tools, shelter, fire – can themselves become a profound advantage.

  12. The history of our evolution is recorded in our DNA. The study of genetic anthropology has just begun as we have, so recently, been able to read this history. It will still be some time before we can interpret it completely, but the answers to these questions will be coming.

  13. There are some interesting comments here related to the sensations that our hairs produce. I tend to look towards the direct survival benefits rather than the pleasurable aspects as being most crucial in evolutionary terms.

    That all humans, irrespective of their adult hair patterns, have the juvenile furlessness trait suggests to me that it did not arise out of long running sexual preferences but arose out of mutation driven variation that survived natural selection; those that had the trait survived and those that didn’t did not. I can’t see our ancestors as being that picky about the hairiness of their partners such that they would reliably have the same preferences across sufficient generations that every human child ended up furless; I suspect that being picky and choosy is a consequence of a large and diverse population. And a preference for less hairy is more likely to be a consequence of juvenile furlessness than causing it.

    It seems like an odd trait to give a distinct survival advantage but when it comes to ectoparasites and disease I can see how it’s possible that it might; better sensory awareness of parasites as well as them being more visible and easy to find and remove could be a big difference if lice borne or tick borne infectious disease were prevalent at a crucial period in hominid evolution. Unlike Godzillatemple I suspect that there was a distinct mutation – a furless mutant form – rather than incremental changes but I don’t know. I’d like to think that Quine is correct and DNA will ultimately answer that question as well as others.

    Phil Rimmer’s comments about pleasant sensations and Pete H about AMSR are interesting. I was not aware of AMSR as a distinct phenomena; but I was going to mention goosebumps and the observation that they appear to enhance and or alter the sensory perceptions arising from disturbance of our hairs. This sounds a lot like a physical manifestation of AMSR or frisson; a kind of sympathetic nervous response links hair follicles all around. Leaving aside the pleasurable aspects I want to point out that my own subjective observation is that goosebumps appear to enhance overall sensitivity and awareness of tactile interactions with our hairs such that even a very small impulse (small bug for example) that would normally be hard to detect sets off sympathetic responses in the hairs across a larger area, that are very easily felt and can’t be ignored. They become sensory amplifiers.

    Goosebumps shouldn’t be seen as vestigial or functionless either BTW; by standing hairs on end they extend the distance beyond the skin that we can feel things to their maximum. They tend to separate the individual hair shafts and that reduces the dampening of deflection/movemen/vibration from hairs being laid against each other, which will make smaller impulses more likely to be felt. AMSR seems to involve pleasurable affects but when it comes to evolution I think the survival factor is going to be more directly important; I think goosebumps probably go back to enhancing sensory awareness during times of fright. Arousal and fright probably involve overlapping neurological responses – multi-functional being the norm in biology – and one piggy backed onto the other.

    AMSR is about pleasant sensations but what we feel with our hairs is also strongly linked to behavioral urges; busy buzzy insects are not just felt, the sensations are very irritating and prompt behaviours to do something to make them stop; to brush, swat, pick the annoying thing OFF! NOW! Consider the human child, who’s fine vellus hairs and sensitive skin make them notice every little bug; the annoying sensations that they can’t ignore get efficiently converted into complaints that parents or older siblings can’t ignore! The end result is reduced exposure to biting bugs, most of all in children.

Leave a Reply