Don't get it (Re: Ape to Man - where did the hair go?)

the lessening of hair noticability could be a product of sexual selection rather than natural selection. humans became very aestetic creatures after they took over from neanderthal.

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the lessening of hair noticability could be a product of sexual selection rather than natural selection. humans became very aestetic creatures after they took over from neanderthal.

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There are many examples of courtship practices that reinforce advantageous characteristics. For example, deer face off mano y mano in a clash of antlers with the winner claiming a harem of does. Therefore, the strongest, and therefore most ablest to defend against predators, wins by using a characteristic that is both sexually and environmentally advantageous. In our near ancestors, the ability to run long distances in the heat was an advantage. Therefore, females made the connection (either counciously, subconsciously, or instincually) that less hair meant more food. If this was a heritable instinct, then women who latched onto hairless men instinctively would make up a larger and larger portion of the population over time until the trait was established population wide.Of course, this is just a hypothesis, but it is one way in which sexual and natural selection can work hand in hand in a way that reinforces environmental fitness.

what does less hair have to do with more food?perhaps it equates less energy put into growing hair and more into growing muscles or brain, but i really don't see the connection.

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what does less hair have to do with more food?

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This was covered earlier in this thread so I'll just give a brief summary. Humans have the ability to run for long distances in extreme heat (95+ F or 35+ celcius). This is due to evaporative cooling by sweat. If we were covered in hair, this evaporative cooling would not be as effective. This allows humans to chase down prey animals for long distances, to the point where the prey animals collapse because of heat exhaustion. At this point, all the hunter has to do is walk up and hit the animal over the head with a stone axe. Therefore, humans have the advantage of eating prey species that can outrun humans in the short term, but lack the endurance due to ineffective body cooling. This type of hunting tactic is used in the open savannahs of Africa.

This is probably out in left field but could our ability to use fire have any bearing on affecting our amount of body hair? The greater the amount of body hair the greater the likelihood of burns and infections in a time when antibiotics were not a common item.Death due to infection would result in selection pressures upon the population if it could be argued that they would perish before reproducing. I do not know enough about the use of fire by early man to tell if this was a possibilty.

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This is probably out in left field but could our ability to use fire have any bearing on affecting our amount of body hair? The greater the amount of body hair the greater the likelihood of burns and infections in a time when antibiotics were not a common item.

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Out of left field as well, but cooking meat could have killed infectious microorganisms in the meat. Plus, you have to catch the animals before you can cook them, therefore less hair would have been linked to hunting before cooking with fire. Of course, this is just my opinion. Could be wrong.

I personally don't think that fire usage started before we were naked apes. I recognize that lack of evidence is not evidence (as in when fire use began), but it seems logical (if evaporative coolong was the trigger) that hair loss would have coincided with the evolution of modern-type body morphology such as in Homo ergaster. While I am sold on the evaporative cooling hypothesis of hair loss, it might not be pointless speculation to look at the selective factors that led to several families of scavenging birds to independantly lose feathers on part of their bodies. I strongly believe that our ancestors may have been good hunters but were excellent scavengers. Another left field point to consider...Here is another WAY left field speculation related to hair loss. It would seem to me that with the selective pressure for hairlessness (I recognize the hair is still there) it would seem to me there would be some social effects because of the importance of grooming in primate societies. I pondered this years ago. One day while reading in the library I found myself being disturbed and very annoyed at a gaggle of undergrads lounging on the library furniture all speaking at once and saying NOTHING, jumping from topic to topic, laughing at inane comments, etc. I noted that this is common behavior (in teens and young adults especially). So, instead of being annoyed I started wondering if idle 'chit-chat' is a grooming substitute in humans. Following this, it would place great selective pressure on the ability to communicate. As I recall from primate literature (no cites, but I believe this is correct) there are individuals who for whatever reason don't groom (or allow themselves to be groomed) or groom poorly etc. These individuals simply do not make it very far in society. This means they also do not leave as many genes behind. If 'chit-chat' is a grooming proxy for a naked ape, it might be possible that those better at it (able to convey more information, able to entertain, etc) had a higher social mobility than those who didn't. It sounds far-fetched, but not so much when you look at how much time non-human primates spend grooming and what grooming means in the social order. I have no delusions that this idea is original, but I haven't encountered it before (in any of the primatology papers I studied to become an invertebrate zoologist )

oh i see.nifty.

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While I am sold on the evaporative cooling hypothesis of hair loss, it might not be pointless speculation to look at the selective factors that led to several families of scavenging birds to independantly lose feathers on part of their bodies. I strongly believe that our ancestors may have been good hunters but were excellent scavengers.

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And . . .

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It would seem to me that with the selective pressure for hairlessness (I recognize the hair is still there) it would seem to me there would be some social effects because of the importance of grooming in primate societies.

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I don't know if you intended these two ideas to be combined, but I can see a way to do just that. In the case of scavenging birds (eg vultures), the lack of feathers probably has to do with keeping excrement and rotting flesh out of the head feathers. In the same way, scavenging humans could have lost their hair for the same reason, keeping foul smelling things out of their fur (by losing the hair). Being that primates are into hygiene, a less "foul" smelling individual may do better in the society. As this trait is established, speech (or nonverbal communication) filled the emotional need that grooming used to fill. Left field is kind of fun once in a while.

Thanks LM! I had not intended those to go together but I see your reasoning. That's intriguing.Another possibility would be that the hairy individuals reeking of scavenged filth would give the clean, chatty primates something to talk about....This message has been edited by Lithodid-Man, 05-27-2004 05:26 PM

My post on the possibility that human communication might be a proxy for social grooming in primates has been done. I did a search on the topic and found a pop sci book by Dr. Robin Dunbar called "Grooming, Gossip, and the Evolution of Language". Just goes to prove "there is no new thing under the sun." - Ecclesiastes 1:9