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?
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?