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  1. 08 Jul '08 13:20 / 8 edits
    I have a theory of why humans evolved to have relatively little body hair compared with most primates.

    I once read about a scientific theory for this that I thought was a bit dubious: it said we evolved to loose our hair because our ancestors used to live by the sea and had to often swim to find sea food such as shellfish etc. If I remember this correctly, the theory goes that having body hair makes this less easy because it produces extra drag as you swim, and, also, when you then come out of the water, the hair stays wet for a while and that means you can suffer from the cold and, also, hair wouldn’t help much to keep us warm while we are in the water anyway. It also pointed out that certain mammals such as dolphins and whales evolved to loose their hair for those reasons.

    The problem I always had with that theory is that dolphins and whales spend all their time in water while other mammals that swim but spend at least part of their lives out of water such as otters, seals, polar bears etc didn’t evolve to loose their hair so, evidently, having hair when swimming couldn’t be that much of a disadvantage -so why would it have been such a disadvantage for our ancestors that must have spent at least some of their time out of water?

    I have now formed an alternative theory: for each species of hairy animal, there is an “optimum length” of hair for heat insulation that that species tends to evolve to have. That optimum is generally determined by the average temperature the animal is normally exposed to. So, not surprisingly, animals that live in cold climates tend to have longer hair than those that live in warm climates. But there is always a biological cost of having that hair even when it is that “optimum length“: when the temperature is hotter than average, that hair will tend to make the animal too hot and increase the risk of heatstroke and therefore will be more of a burden than a help to survival in hotter than average weather.

    At some stage in our evolution, our ancestors must have evolved to have the intelligence to wear clothes in cold weather and then did just that. Now suppose the optimum length of hair just before our ancestors started wearing clothes in cold weather was, say, one inch long. That would have resulted in our assistors evolving to have about one-inch long hair covering most of the area of their bodies. That would have meant that:

    1, when the temperature was below average, the hair didn’t give the optimum amount of insulation and they suffered from the cold

    2, when the temperature was average then the hair was just the right length to make them feel comfortable

    3, when the temperature was above average then the hair was too long making them suffer from the heat and also increasing the risk of death through heatstroke.

    But now consider this: what would be the optimum length of hair once our ancestors started wearing clothes whenever they felt too cold?

    For a person that has almost no hair but wears cloths when he feels too cold:

    1, when the temperature is below average, the almost hairless person will respond by putting a lot of extra thick cloths on and so he wouldn’t suffer from the cold

    2, when the temperature is average then the almost hairless person would respond by putting just a thin layer of cloths -just enough to make him feel comfortable

    3, when the temperature is above average then the almost hairless person would respond by putting on no cloths to take full advantage of the fact that a naked relatively hairless body is better at expelling excess heat thus he suffers less from the heat and also has minimal risk of death through heatstroke.

    And if you compare that for a person that has one-inch long hair but wears cloths when he feels too cold:

    1, when the temperature is below average, the hair doesn’t give the optimum amount of insulation so he responds by supplementing the insulation with a thin layer of clothes -just enough to make him feel comfortable.

    2, when the temperature is average then the hair is just the right length to make him feel comfortable -so he wears no clothes.

    3, when the temperature is above average then his hair is too long making them suffer from the heat and also increasing the risk of death through heatstroke even though he wears no clothes when it is hot.

    It is clear from the above that the person that is almost hairless and wears clothes in response to feeling too cold has a definite survival advantage over the person that has one-inch long hair over most of his body and wears clothes in response to feeling too cold. Therefore, natural selection will select for those people that have almost no hair once they start wearing clothes when they feel cold and this is why we evolved to have relatively little hair. Hence, by theory says that wearing clothes made us loose our hair (through evolution).

    I suspect we kept the long hair on top of our heads to help protect the top of our heads from lethal amounts of sunburn as it would be that part of the body that would be most exposed to UV radiation if we were completely hairless and naked in hot weather.

    Any comments about my theory?
  2. 08 Jul '08 14:25
    Then why do various native types that never started wearing more than a loin cloth have almost have no body hair?
  3. Standard member forkedknight
    Defend the Universe
    08 Jul '08 15:15
    Originally posted by Sam The Sham
    Then why do various native types that never started wearing more than a loin cloth have almost have no body hair?
    They tend to live in tropical regions...

    Why do they need more clothes? Body hair would be a liablility in the tropics.
  4. 08 Jul '08 21:17
    Originally posted by forkedknight
    They tend to live in tropical regions...

    Why do they need more clothes? Body hair would be a liablility in the tropics.
    Like it is for all the other mammals in the tropics? the other great apes? the big cats? Deer, buffalo, et etc?

    I don't think the theory really stands up, though I also don't have a better one!

    --- Penguin.
  5. 08 Jul '08 21:28 / 1 edit
    The water theories, does that explain why my father has no hair on his head...? He certainly has facial hair.
  6. 09 Jul '08 01:01
    Originally posted by Andrew Hamilton
    I have a theory of why humans evolved to have relatively little body hair compared with most primates.

    I once read about a scientific theory for this that I thought was a bit dubious: it said we evolved to loose our hair because our ancestors used to live by the sea and had to often swim to find sea food such as shellfish etc. If I remember this ...[text shortened]... ation if we were completely hairless and naked in hot weather.

    Any comments about my theory?
    Sounds more like a hypothesis that you need to start testing......
  7. 09 Jul '08 08:56
    Originally posted by timebombted
    Sounds more like a hypothesis that you need to start testing......
    Unfortunately, I see no practical way my hypothesis can be “tested” -at least not in the “physical” sense -I mean, how could the fossil evidence possibly confirm or refute my hypothesis -especially when you consider the fact that hair is not normally preserved in the fossils of our ancestors!

    I have to make do with the weaker position of claiming that, although I don’t think my hypothesis can be “proven”, I think my hypothesis is the one most probable to be correct because I assume that there is no better alternative hypothesis -and the best way somebody can demonstrate to me that I am wrong (at least about that) is to came up with an alternative hypothesis which makes at least as much “sense” as my own.
  8. 09 Jul '08 11:45 / 1 edit
    Originally posted by Andrew Hamilton
    Unfortunately, I see no practical way my hypothesis can be “tested” -at least not in the “physical” sense -I mean, how could the fossil evidence possibly confirm or refute my hypothesis -especially when you consider the fact that hair is not normally preserved in the fossils of our ancestors!

    I have to make do with the weaker position of claiming ...[text shortened]... to came up with an alternative hypothesis which makes at least as much “sense” as my own.
    Another competing hypothesis could be through sexual selection. I have not thought deeply about it but it can account for features that would otherwise be thought of as detrimental to the survival of the individual. One of the obvious examples of this is the peacocks tail.

    --- Penguin.
  9. Standard member flexmore
    Quack Quack Quack !
    09 Jul '08 12:40 / 7 edits
    Originally posted by Andrew Hamilton
    I have a theory of why humans evolved to have relatively little body hair compared with most primates.

    I once read about a scientific theory for this that I thought was a bit dubious: it said we evolved to loose our hair because our ancestors used to live by the sea and had to often swim to find sea food such as shellfish etc. If I remember this ...[text shortened]... ation if we were completely hairless and naked in hot weather.

    Any comments about my theory?
    I like it: the amazing incredible power of clothing.

    to increase the power of your theory:

    people with long hair get nits/bugs/pests breeding in the hair and suffer diseases ... people with clothes can chuck the infested clothes out and move on.

    people with clothes, if being chased, can drop the clothes as a decoy and escape while the pursuers examine the clothes - then they get another chance.

    people who get used to using clothing get used to using all sorts of things and use more tools: rocks/sticks etc.

    and as you say, the power of warmth will be primary in many places: they carry their bed with them

    when i looked in wikipedia they seem to go the other way round .. trying to use the dating of lice to date the use of clothes assuming lice need clothes to live in ...

    i think you have a very interesting idea .. maybe clothes are a lot older than many people assume. instead of people losing hair and then needing clothes .. they might have gained clothes and then lost hair.
  10. 09 Jul '08 14:27
    Originally posted by Andrew Hamilton
    Any comments about my theory?
    I think you would need to establish when people started wearing clothes.

    Other possibilities are fire and shelter. If man found other ways (than hair) to keep warm at night then they might not have needed hair. Hair has disadvantages.

    It could even have been something odd like man evolving a defence against a specific disease - say a tick borne disease.

    I also wouldn't dismiss the water ape theory so easily. There are places where baboons and other apes spend quite a lot of time in the water - swamps rather than the sea. Also we have other features common amongst water creatures such as a layer of insulating fat - though that might be simply due to our lack of hair. (and you forgot to mention the Hippo in your list).


    Another possibility might be the decreased effect of sunlight due to man walking vertically, reduces the need for hair, or maybe man became more active and needed more efficient cooling system.
    Remember that man evolved from a largely vegetarian ape to a bit of a carnivore.
  11. 09 Jul '08 18:36 / 1 edit
    Originally posted by twhitehead
    I think you would need to establish when people started wearing clothes.

    Other possibilities are fire and shelter. If man found other ways (than hair) to keep warm at night then they might not have needed hair. Hair has disadvantages.

    It could even have been something odd like man evolving a defence against a specific disease - say a tick borne dise oling system.
    Remember that man evolved from a largely vegetarian ape to a bit of a carnivore.
    …Other possibilities are fire and shelter. If man found other ways (than hair) to keep warm at night then they might not have needed hair.…

    I think you have made several good point -but especially the above one! I think I will have to make my theory more complex to take into account the effect of the invention of fire and shelter as well as clothes and say it could have been any one of these or any combination of them that resulted in us loosing our hair.
  12. 09 Jul '08 19:12 / 3 edits
    Originally posted by Penguin
    Another competing hypothesis could be through sexual selection. I have not thought deeply about it but it can account for features that would otherwise be thought of as detrimental to the survival of the individual. One of the obvious examples of this is the peacocks tail.

    --- Penguin.
    An interesting hypotheses -but I think I see a problem with it:

    Which one evolved first:

    1, “the instinct for the bias of choosing which ever potential mate has the least amount of hair”

    2, “the lack of hair”

    If we pose a similar question for the case of sex selection in peacocks:

    Which one evolved first:

    1, “the instinct for the bias of choosing which ever potential mate has the most impressive looking tail”

    2, “the impressive looking tail”

    This is easy to answer:
    “the instinct for the bias of choosing which ever potential mate has the most impressive looking tail” came first because those males with the most impressive looking tail would be those that are most likely to be the generally healthier ones (general good health probably would make virtually every part of the body look more impressive but, by an accident of evolution, probably due to a single mutation, caused the females instinct to focus on a particular aspect or aspects of the tail) and only then natural selection made the tail look ever more impressive.

    But, for sex selection humans, I guess it wouldn’t make sense for:
    “the instinct for the bias of choosing which ever potential mate has the least amount of hair”
    to come first because, I would guess that the lack of hair would actually indicate the potential mate would be LESS healthy and not more healthy! That is because disease and other health problems often cause partial or total hair loss. Therefore, if I am right about that, all the time our ancestors had lots of hair, natural selection would actually select AGAINST and not for
    “the instinct for the bias of choosing which ever potential mate has the least amount of hair” !

    Therefore, I conclude that “the lack of hair” came first but then that would beg the question of what caused it if
    “the instinct for the bias of choosing which ever potential mate has the least amount of hair”
    came AFTER the evolution of “the lack of hair”!
  13. Subscriber AThousandYoung
    Do ya think?
    09 Jul '08 20:03
    I read about the Water Ape hypothesis in Desmond Morris' influential but discredited book The Naked Ape. In that book he points out that the hairs on the back are oriented in the direction of water flow when a person is swimming, which is not true for many other animals.
  14. 09 Jul '08 20:33 / 1 edit
    Originally posted by AThousandYoung
    I read about the Water Ape hypothesis in Desmond Morris' influential but discredited book The Naked Ape. In that book he points out that the hairs on the back are oriented in the direction of water flow when a person is swimming, which is not true for many other animals.
    …the hairs on the back are oriented in the direction of water flow when a person is swimming, which is not true for many other animals.

    Wrong! Some (not all) other animals that don’t swim particularly often have hairs in the direction of water flow! -as clearly can be seen if you look at the hairs on the back of this picture of a Chimpanzee:
    http://www.acclaimimages.com/_gallery/_pages/0061-0507-2114-0215.html

    I am sure other examples can be found.

    Incidentally, watch out! Chimpanzees are learning to fight back!:
    http://www.freakingnews.com/Chimpanzee-Pictures-33414.asp
  15. 09 Jul '08 23:12
    Originally posted by Andrew Hamilton
    Unfortunately, I see no practical way my hypothesis can be “tested” -at least not in the “physical” sense -I mean, how could the fossil evidence possibly confirm or refute my hypothesis -especially when you consider the fact that hair is not normally preserved in the fossils of our ancestors!

    I have to make do with the weaker position of claiming ...[text shortened]... to came up with an alternative hypothesis which makes at least as much “sense” as my own.
    You could at least start testing for the optimum length:average temperature you talk about........