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Why are we naked?

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Ugh... Ever notice its always people who are balding/bald who make that statement?

 

I AM NOT BALD!!!!

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So basically my opinion is that hair insulates the body from exposure to the outside air's convection currents and reduces the amount of evaporation that is needed for a sweat-based cooling system that was essential to our adaptation to the dryer savanna environment.

 

I dont think this is complete. When compared with other animals on the savanah, the only others with little hair are the very large ones, elephants, hippos, rhinos.

 

Yet there are smaller creatures, such as lions, zebra and buffalo which still have fur. They are larger creatures than humans, and so should have more of a problem with radiating out that excess heat. Buffalo and other herd animals in particular will often walk for days or weeks at a time between feeding grounds, so its not as though humans would be more physically active than these animals. I'm tempted by Martins brain heat idea, but losing almost all of our hair just to compensate for our increase in brain size seems a bit extreme. A link would be helpful.

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']I dont think this is complete. When compared with other animals on the savanah' date=' the only others with little hair are the very large ones, elephants, hippos, rhinos.

 

Yet there are smaller creatures, such as lions, zebra and buffalo which still have fur. They are larger creatures than humans, and so should have more of a problem with radiating out that excess heat. Buffalo and other herd animals in particular will often walk for days or weeks at a time between feeding grounds, so its not as though humans would be more physically active than these animals. I'm tempted by Martins brain heat idea, but losing almost all of our hair just to compensate for our increase in brain size seems a bit extreme. A link would be helpful.[/quote']

 

Hi Tycho, since you asked about a link here is something

http://www.economist.com/science/displayStory.cfm?story_id=2281888

 

It argues that the heat theory (which used to be have some currency) has been set aside in favor of the lice theory.

 

It does quote someone who still likes the heat theory.

 

It seems to conclude that there is no consensus about this among human evolutionary biologists. they havent settled on one explanation yet.

 

this is just one journalist's view, I will keep an eye out for other discussions of this

 

EDIT: more support for lice

http://news.bbc.co.uk/1/hi/sci/tech/2975914.stm

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']I dont think this is complete. When compared with other animals on the savanah' date=' the only others with little hair are the very large ones, elephants, hippos, rhinos.

 

Yet there are smaller creatures, such as lions, zebra and buffalo which still have fur. They are larger creatures than humans, and so should have more of a problem with radiating out that excess heat. Buffalo and other herd animals in particular will often walk for days or weeks at a time between feeding grounds, so its not as though humans would be more physically active than these animals. I'm tempted by Martins brain heat idea, but losing almost all of our hair just to compensate for our increase in brain size seems a bit extreme. A link would be helpful.[/quote']

I have thought about this a little bit and I am more convinced than ever that hominids lost their hair in order to lessen the strain of reducing excess body heat.

 

Hair reduces the body’s ability to cool itself by reducing the cooling capacity of:

 

1) Convection

2) Evaporation/Sweating

 

The Savanna environment required more efficient means for the hominids to cool themselves because:

 

1) The increase in body temperature due to direct sun radiation

2) The greater distances traveled during scavenging compared to the lush jungle.

3) The need to run from predators.

4) Evaporation/sweating became incredibly more efficient in the dry Savanna environment and hair interferes with the heat reduction from sweating.

 

Some other savanna animals didn't require as much heat reduction efficiency from sweating as hominids, and thus didn't benefit as greatly from total hair loss because:

 

1) They pant, which is an effective means of heat reduction for many animals, but not hominids.

2) They were nocturnal while man is usually active during the day.

3) They had more efficient gaits. Animals like lions and zebras have graceful and energy efficient walks and runs, while early hominids were still adjusting to walking greater distances and walking semi to fully effect on two feet. This means that animals like Zebras expelled less energy for equal amounts of effort.

4) They had smaller brains. Brains require a lot of energy per weight and the hominids were already developing great brain to body size ratios compared to other animals. The modern human brain uses 25% of the body's energy and therefore generates 25% of its heat while only weighing about 3 pounds.

5) Other animals have evolved other methods to cool themselves, like wading in mud.

 

Additional reasoning:

 

1) Chimpanzees and apes have very sparse hair density compared to other mammals with hair. The amount of hair reduction through shortening is comparable to the amount of hair reduction and shortening in other savanna animals, compared to their colder climate counterparts. As an example I provide a link that has pictures of African dogs and cold climate wolves and a picture of chimpanzees, so that you can observe the differences in hair density: http://www.denverzoo.org/animalsplants/mammal02.htm

Chimpanzee%20485083.jpg

 

2) Evolution has no foresight, nor is it perfect. While developing denser yet shorter hair like many other savanna animals may have been the most optimal choice for man, evolution does not plan out its strategies. Natural selection selects most strongly for the characteristics that are influencing survival and procreation the greatest at that moment in time. Men were dying because of heat exhaustion and lack of endurance because of the extreme heat so Mother Nature selected men with shorter, thinner hair for survival.

 

3) Men eventually developed the intelligence and knowledge required to make clothing and shield himself from the cold. At one point in time man had a very efficient means to protect himself from the cold, but no means to efficiently protect himself from the heat. Animal skins were a removable replacement for the warmth of hair and thus removed one of hairs greatest benefits.

 

Criticism for the lice theory:

 

1) Most land mammals are exposed to vermin like lice and flees. We know that hair makes infestations worse because it provides an environment favorable for breeding, hiding, and holding on to. However, regardless of the negative effects of vermin like lice, most mammals still have hair because the temperature regulation benefits of hair trumps the problems associated with it.

 

2) Since chimpanzees already have an effective means to remove lice, from grooming, it is likely that man's ancestor also used similar methods to remove lice. Since man's ancestor already had means to hold lice infestations in check, the selection for genes that reduced the deaths associated from infestations would not be strong so it is less likely that lice infestations were the biggest factor for the hair reduction of hominids.

 

3) No apes that I'm aware of have lost their hair like humans, yet they are constantly exposed to lice. If hair was causing more problems from lice than it solved it, we would probably see more naked ape species.

 

4) Jungle environments are fertile grounds for lice. I don't believe that hominids experienced more problems with lice after they moved to the savanna. But hominids definitely had problems with heat after he moved to the savanna. Furthermore, we see a clear correlation between other animals’ amount of hair and the temperature. So we see a clear correlation between temperature and hair, but no correlation between lice and hair.

 

Criticism of the Aquatic Ape theory:

 

We have found many fossils of Homo erectus around coastland. In fact, it seems like he spread out following the coast. However, hominids probably did not loose their hair do to the effects of the ocean.

 

1) Hominids were beach combers, not ocean swimmers. Homo erectus used stone tools, so cracking open crab and oyster shells probably provided a useful sustenance. But combing the beach is not the same as living in the ocean and water adaptations like loosing hair would not have occurred.

 

2) Hominids spent very little time in the water swimming. Hominids had no reason to spend more than a little time in the ocean because they were probably at least as bad at swimming as we are. They couldn't catch any fish with their hands and the amount of time spent in the ocean diving for clams and such was probably not significant enough to cause radical changes.

 

3) Hominids don't have obvious adaptations to water but they have obvious adaptations to heat. We don't have webbed feet or sea-water resistant skin, but we do have a lot of sweat glands. Chimpanzees don't have near the capacity to sweat that humans do, so it was very important at one point to be able to cool down. We don't find these same kinds of obvious adaptations to spending a great deal of time in the water.

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I'm surprised that no one has brought up the speech theory. This is the one I'm most familiar with.

The general idea is that panting is an ineffective way of loosing heat for humans since it interferes with speech. How are you supposed to talk properly when you have to pant constantly to loose heat? So the idea is that we lost our hair to allow us to sweat instead to loose heat freeing up our mouths for speech.

 

We all know how impossible it is to talk after running alot and having to breath havily to catch your breath. Now imagine breathing like that all day on a hot day and trying to have a conversation.

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there are a lot of reasons i see to us losing our hair. i think another is because we are capable of cutting off the skin of another animal with fur to keep us warm in the cold. And only our heads poked out so maybe thats why we have a lot of hair on our heads too.

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Is it possible that our use of fire had something to do with it? This seems to make some sense because animals who were particularly furry would have some difficulty with safely manipulating fire without setting themselves alight, whereas, at the same time, most would try to keep their head and their genitals well away from fire, which would account for the hair that remains.

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Is it possible that our use of fire had something to do with it? This seems to make some sense because animals who were particularly furry would have some difficulty with safely manipulating fire without setting themselves alight, whereas, at the same time, most would try to keep their head and their genitals well away from fire, which would account for the hair that remains.

 

The trouble with this, or any other bit of human technology, means that we lost our hair in quite a short time period.

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I think the key is neotony, retention of juvenile characteristics in the adults of a species. Incidentally, baby apes look like human (less hair). The development of primates' brains halts after birth while the brain of humans continue to grow until near maturity. Our sparse body hair and enlarged heads are reminiscent of baby primates. maybe the lack of body hair is a side effect of neotony? (perhaps caused by a mutation of a certain gene, causing us to exhibit this growth feature) Another fact to note is that we share around 95%(not sure) of our DNA to primates like gorillas.

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I think the key is neotony, retention of juvenile characteristics in the adults of a species. Incidentally, baby apes look like human (less hair). The development of primates' brains halts after birth while the brain of humans continue to grow until near maturity. Our sparse body hair and enlarged heads are reminiscent of baby primates. maybe the lack of body hair is a side effect of neotony? (perhaps caused by a mutation of a certain gene, causing us to exhibit this growth feature) Another fact to note is that we share around 95%(not sure) of our DNA to primates like gorillas.

 

TWJian, I remember when you were doing pheromones in ants. and asking about strategy/tactics.

 

Let me see if I can paraphrase what you are saying about neoteny and hairlessness.

we look like SCALED-UP ape-babies with proportionately big heads like them and not much hair like them

and it is called NEOTENY, and it is obtained by changing some genes that affect how the timer clock ticks-----the timer that controls several aspects of ape maturation.

 

by changing one or a few genes you can change a biological clock and that will cause SEVERAL different effects----a mutation in the clock will get you a BUNDLE OF CHANGES, maybe not all are good, maybe some are neutral, but if at least one confers a significant advantage then there will be selection (for the whole bundle).

 

so hairlessness might be an ACCIDENT that came along in the same bundle with a big brain

 

 

for instance, at some point in maturation an ape child's brain stops growing and the body gets big and strong and hairy. if you can DELAY that moment when the brain stops growing along with the rest then ALSO delays the moment of getting all hairy, but you end up with a bigger brain, OK ---- you stay more looking like an ape baby which has less hair and a proportionately big head----the big head was what was driving selection of the gene because it confered advantage and the hairlessness was just an accidental BYPRODUCT.

 

interesting. has Skye or Mokele discussed this somewhere?

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It's certainly very possible. I do recall that our pattern of hair is neotenic, so it's certainly possible that, rather than an adaptation, our comparative hairlessness is merely an evolutionary side-effect of a different adaptation.

 

Mokel

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Someone above commented regarding the AAT "On the surface, perhaps, but they don't stand up to scrutiny. Here is a critique."

 

I'd just like to point out that the critique we are guided to is totally full of holes. It also contains loads stuff that sounds like it makes a point but doesn't, e.g.,

 

"So contrary to the AAT claim, humans are not the only non-aquatic mammal which can hold its breath. Various monkeys, for instance, can and do hold their breath, and so do dogs. (Another common and related AAT claim is that non-aquatic animals have no control over their vocalizations, which should also surprise any dog owner.) "

 

AAT says that apes cannot hold their breath. Apes are completely unable to hold their breath - even chimps cannot do this. Interestingly dolphins are unable to breath unconsiously. We are in between, being able to hold our breath and breath unconsiously.

 

The only animal so far recorded able to utter human speech using the same mechanisms as a human (so birds don't count) was a sealion that had been kept in captivity. I have heard it speak and it sounds like a human - really wierd! It's ability is dependant on it being able to control its breath in a way only aquatic animals (and humans) are capable of.

 

Without going on and on about the many innacuracies in this critique (its like reading one of those critiques on evolution by a believer in intelligent design!) I'll just say that one should be aware that many of the arguments presented are based on a false understanding of the AAT, and backed up by irrelevant scientific studies.

 

AAT is going to be the new paradigm, so get on board!

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Thought I'd post my summary of what Dawkins had to say:

 

After humans started wearing clothing, hair became less important, and something of a disadvantage because it provided a habitat for parasites. So once clothing could keep us warm the loss of hair was favored by natural selection because it minimized the amount of time humans had to spend picking parasites out of their hair (something other primates spend inordinate amounts of time doing)

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'']The trouble with this, or any other bit of human technology, means that we lost our hair in quite a short time period.

 

Dawkins gave instances of various mammals being bread for a complete absence of hair in two dozen generations or less.

 

If the parasite theory was true, it could be easily combined with sexual selection: hair fell out of favor because the more hairless individuals found hairy, parasite covered bodies disgusting or otherwise unattractive.

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The parasite idea is unlikely to be the reason. It would apply equally to apes and they still have hair. Also, they are usually picking off salt crystals from each other - not ticks and fleas as is commonly thought.

 

Human evolution is, however, mostly due to sexual selection. The question is why were certain features thought of as sexy? Someone earlier made the point about hairlessness being a by product of having a big brain and I think that is at least partly correct. But having a big brain would be an advantage to any ape, so why didn't chimps and other apes get bigger brains when we did? Something happened around 5 million years ago that made us get big brains but didn't work for other apes.

 

There is the Omega 3 fatty acid arguement which I am sure is correct, and seafood is rich in Omega 3. That might have been enough, but somehow I think it would have required more. I think a semi-aquatic lifestyle pushed our ancestors into liking neotenic features. Dolphins, Whales, seals, sealions, otters, elephants, hippos, - all exhibit neotenic features to varying degrees, as it is helpful for an aquatic (or semi aquatic) lifestyle. Once pushed in a certain direction, sexual selection has done the rest and our brains have got bigger and bigger - and will continue to do so as sexual selection is still occurring and we humans still find neotenic features attractive.

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I have thought about this a little bit and I am more convinced than ever that hominids lost their hair in order to lessen the strain of reducing excess body heat.

 

Hair reduces the body’s ability to cool itself by reducing the cooling capacity of:

 

1) Convection

2) Evaporation/Sweating

 

The Savanna environment required more efficient means for the hominids to cool themselves because:

 

1) The increase in body temperature due to direct sun radiation

2) The greater distances traveled during scavenging compared to the lush jungle.

3) The need to run from predators.

4) Evaporation/sweating became incredibly more efficient in the dry Savanna environment and hair interferes with the heat reduction from sweating.

 

Some other savanna animals didn't require as much heat reduction efficiency from sweating as hominids' date=' and thus didn't benefit as greatly from total hair loss because:

 

1) They pant, which is an effective means of heat reduction for many animals, but not hominids.

2) They were nocturnal while man is usually active during the day.

3) They had more efficient gaits. Animals like lions and zebras have graceful and energy efficient walks and runs, while early hominids were still adjusting to walking greater distances and walking semi to fully effect on two feet. This means that animals like Zebras expelled less energy for equal amounts of effort.

4) They had smaller brains. Brains require a lot of energy per weight and the hominids were already developing great brain to body size ratios compared to other animals. The modern human brain uses 25% of the body's energy and therefore generates 25% of its heat while only weighing about 3 pounds.

5) Other animals have evolved other methods to cool themselves, like wading in mud.

 

Additional reasoning:

 

1) Chimpanzees and apes have very sparse hair density compared to other mammals with hair. The amount of hair reduction through shortening is comparable to the amount of hair reduction and shortening in other savanna animals, compared to their colder climate counterparts. As an example I provide a link that has pictures of African dogs and cold climate wolves and a picture of chimpanzees, so that you can observe the differences in hair density: http://www.denverzoo.org/animalsplants/mammal02.htm

[img']http://www.exzooberance.com/virtual%20zoo/they%20walk/chimpanzee/Chimpanzee%20485083.jpg[/img]

 

2) Evolution has no foresight, nor is it perfect. While developing denser yet shorter hair like many other savanna animals may have been the most optimal choice for man, evolution does not plan out its strategies. Natural selection selects most strongly for the characteristics that are influencing survival and procreation the greatest at that moment in time. Men were dying because of heat exhaustion and lack of endurance because of the extreme heat so Mother Nature selected men with shorter, thinner hair for survival.

 

3) Men eventually developed the intelligence and knowledge required to make clothing and shield himself from the cold. At one point in time man had a very efficient means to protect himself from the cold, but no means to efficiently protect himself from the heat. Animal skins were a removable replacement for the warmth of hair and thus removed one of hairs greatest benefits.

 

Criticism for the lice theory:

 

1) Most land mammals are exposed to vermin like lice and flees. We know that hair makes infestations worse because it provides an environment favorable for breeding, hiding, and holding on to. However, regardless of the negative effects of vermin like lice, most mammals still have hair because the temperature regulation benefits of hair trumps the problems associated with it.

 

2) Since chimpanzees already have an effective means to remove lice, from grooming, it is likely that man's ancestor also used similar methods to remove lice. Since man's ancestor already had means to hold lice infestations in check, the selection for genes that reduced the deaths associated from infestations would not be strong so it is less likely that lice infestations were the biggest factor for the hair reduction of hominids.

 

3) No apes that I'm aware of have lost their hair like humans, yet they are constantly exposed to lice. If hair was causing more problems from lice than it solved it, we would probably see more naked ape species.

 

4) Jungle environments are fertile grounds for lice. I don't believe that hominids experienced more problems with lice after they moved to the savanna. But hominids definitely had problems with heat after he moved to the savanna. Furthermore, we see a clear correlation between other animals’ amount of hair and the temperature. So we see a clear correlation between temperature and hair, but no correlation between lice and hair.

 

Criticism of the Aquatic Ape theory:

 

We have found many fossils of Homo erectus around coastland. In fact, it seems like he spread out following the coast. However, hominids probably did not loose their hair do to the effects of the ocean.

 

1) Hominids were beach combers, not ocean swimmers. Homo erectus used stone tools, so cracking open crab and oyster shells probably provided a useful sustenance. But combing the beach is not the same as living in the ocean and water adaptations like loosing hair would not have occurred.

 

2) Hominids spent very little time in the water swimming. Hominids had no reason to spend more than a little time in the ocean because they were probably at least as bad at swimming as we are. They couldn't catch any fish with their hands and the amount of time spent in the ocean diving for clams and such was probably not significant enough to cause radical changes.

 

3) Hominids don't have obvious adaptations to water but they have obvious adaptations to heat. We don't have webbed feet or sea-water resistant skin, but we do have a lot of sweat glands. Chimpanzees don't have near the capacity to sweat that humans do, so it was very important at one point to be able to cool down. We don't find these same kinds of obvious adaptations to spending a great deal of time in the water.

 

A few points in no real order:

 

If losing heat was the reason, our heads would have been the first place to lose it and bald men would be seen as extremely sexy!

 

Re: Aquatic ape theory:

 

Points 1 and 2) We would have lost our hair long before Homo erectus evolved. Think of the common ancestor of us and chimps - its around then it would have happened.

 

3) We have flipper shaped feet - great for swimming and also pre-adapted for life on land. We also have a nose that stops water going straight up the nostrils. We can hold our breath. If we lie still in water we naturally float with our mouth and nose just above water. Human babies can swim as soon as they are born (they really can!). Lots more stuff that I won't go into here!

 

Sweating is a great way to lose heat on a savannah once you are a bipedal hairless ape with the intelligence to carry water with you (or dig to find it). Its a crap way to lose heat otherwise as one dies of dehydration very quickly. I doubt it would have evolved just as a result of being on a savanah.

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AAT says that apes cannot hold their breath. Apes are completely unable to hold their breath - even chimps cannot do this.

 

So, let me get this straight: Someone points out that non-aqautic apes and monkeys (and even dogs) can hold their breath, which casts doubts on the AAH, and you respond by asserting they can't because of the AAH? You're kidding, right?

 

Sorry, but evidence takes precedence over theory. If data shows that non-aquatic apes can hold their breath, that punches some big holes in the AAT, which cannot be circumvented by simply denying the data.

 

Without going on and on about the many innacuracies in this critique (its like reading one of those critiques on evolution by a believer in intelligent design!) I'll just say that one should be aware that many of the arguments presented are based on a false understanding of the AAT, and backed up by irrelevant scientific studies.

 

This coming from someone who wants to ignore evidence because it conflicts with their pet hypothesis?

 

And, FYI, it's a hypothesis, not a theory. Only once fossil evidence supports it will it become a theory.

 

Dolphins, Whales, seals, sealions, otters, elephants, hippos, - all exhibit neotenic features to varying degrees, as it is helpful for an aquatic (or semi aquatic) lifestyle.

 

Please support this assertion. The only animals I am aware of which undergo neoteny in response to adapting to an aqautic life are salamanders. Even reptiles don't.

 

Points 1 and 2) We would have lost our hair long before Homo erectus evolved. Think of the common ancestor of us and chimps - its around then it would have happened.

 

Given that there is no fossil evidence concerning the hairiness of any hominin, that cannot be used to support any theory. Hair may have been lost immediately after the split or only after H. sapiens evolved; we have no fossil skin impressions to tell us anything more.

 

We have flipper shaped feet - great for swimming and also pre-adapted for life on land.

 

You've got it wrong-way around. We have flipped-shpaed feet because feet evolved *from* flippers, back in the Devonian when vertebrates first crawled out of the sea.

 

We also have a nose that stops water going straight up the nostrils.

 

Wrong. Valves that seal the nostrils are a *VERY* common adapation, seen is just about every aquatic and amphibious species. Why don't we have them?

 

We can hold our breath.

 

So can dogs, and they're *definitely* not adapted for an aquatic life.

 

If we lie still in water we naturally float with our mouth and nose just above water.

 

Actually, we naturally float face down. See corpses.

 

Its a crap way to lose heat otherwise as one dies of dehydration very quickly. I doubt it would have evolved just as a result of being on a savanah.

 

I don't think sweating as actually any worse than any other method mammals use. Panting and sweating *both* use evaporative cooling, so you'll need to dump just as much water either way.

 

Mokele

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So' date=' let me get this straight: Someone points out that non-aqautic apes and monkeys (and even dogs) can hold their breath, which casts doubts on the AAH, and you respond by asserting they can't because of the AAH? You're kidding, right?

 

Sorry, but evidence takes precedence over theory. If data shows that non-aquatic apes can hold their breath, that punches some big holes in the AAT, which cannot be circumvented by simply denying the data.

 

No, I am not saying that. I am simply saying that the AAT refers to apes, our closest ancestors, not other animals, so the studies referred to are irrelevant in that sense. You'd need to prove that chimps can hold their breath voluntarily under water - and exhibit a dive response while your at it. We all know other animals can e.g. seals, otters, mink, water voles etc.

 

This coming from someone who wants to ignore evidence because it conflicts with their pet hypothesis?

 

And' date=' FYI, it's a hypothesis, not a theory. Only once fossil evidence supports it will it become a theory.

 

Not my pet hypothesis at all - just more likely than the savannah theory (on its own that is - I am sure the savannah theory is part of the story). Also it does not need fossil evidence to be a theory - any evidence will do! It was not fossil evidence that makes evolution a theory because the fossils themselves prove nothing - its just how they are interpreted - which is open to question - ask a ID proponent!

 

Please support this assertion. The only animals I am aware of which undergo neoteny in response to adapting to an aqautic life are salamanders. Even reptiles don't.

 

 

You are confusing 'metamorphic' neoteny and evolutionary neoteny. Evolution can 'use' neoteny to get a result e.g' date=' to get a big brain, resemble an infant (in proportion) which has a bigger brain compared to the body than adults. Or, need fins instead of legs? Simply have shorter legs in comparison to your body (like infants) and over millions of years you turn into a dolphin, or whale, or whatever. If you don't understand what I'm going on about please read up on it. Some say it is an alternative theory for human evolution, but its more of a process than a complete theory because it needs a reason to work. it can be incorporated into both the savannah and aquatic ape theories.

 

Given that there is no fossil evidence concerning the hairiness of any hominin, that cannot be used to support any theory. Hair may have been lost immediately after the split or only after H. sapiens evolved; we have no fossil skin impressions to tell us anything more.

 

Yes I know that' date=' I am just saying what the AAT requires. Obviously we don't know when we lost our hair, but if it the AAT were true, the hair loss would have most probably occurred way before Homo erectus evolved. That's all I'm saying.

 

You've got it wrong-way around. We have flipped-shpaed feet because feet evolved *from* flippers, back in the Devonian when vertebrates first crawled out of the sea.

 

You seem to be showing a lack of knowledge about evolution. The 'aquatic ape' would have started with feet like chimps' date=' or gorollas. However, in one sense you are right. By 'using' neoteny we could have reverted back to 'embryonic' feet which would have resembled our very distant fishy ancestors.

 

Wrong. Valves that seal the nostrils are a *VERY* common adapation, seen is just about every aquatic and amphibious species. Why don't we have them?

 

Seals are almost totally aquatic so have evolved 'closable' nostrils as they have been aquatic for a very long time. We would not have been aquatic (or semi aquatic actually) for very long. Maybe if we had stayed in the water for a few more million years we would have developed closable nostrils. Humans only got as far as a nose that has a 'flap' at the front to stop water entering when swimming. Actually' date=' the proboscis monkey is a relatively good swimmer (for a primate) and has a big nose as well!

 

 

 

So can dogs, and they're *definitely* not adapted for an aquatic life.

 

We are not adapted for an aquatic lifestyle nor were our 'aquatic' ancestors adapted for a life totally in water! We would have just developed some minor characteristics that helped a little. e.g. flipper like feet (but not flippers)' date=' subcutaneous fat (but not blubber), a long nose (but not closable nostrils) ability to hold our breath and have a dive response (but not anywhere near as well as a seal or dolphin) etc... I think you misunderstand the Aquatic Ape Theory! Maybe it should be renamed the 'semi-aquatic ape theory', or to really clear the 'ape that spent very long periods of time in water theory'.

 

 

 

Actually, we naturally float face down. See corpses.

 

Corpses are dead. Even dead dolphins just float about on the surface. On still water a human can lie on its back and its head tilts naturally back leaving the nose and mouth above water. Try it next time you swim' date=' just relax and it happens! This is actually a well known fact - nothing to do with the AAT theory as it was known way before.

 

 

 

I don't think sweating as actually any worse than any other method mammals use. Panting and sweating *both* use evaporative cooling, so you'll need to dump just as much water either way.Mokele

 

Yeah, but panting can be controlled when things get tough. Sweating can't. Also, the amount of water lost through panting is nowhere near what humans lose through sweating. As I said, sweating is a brilliant way of losing heat quickly, even better if hairless, but only good if you can carry water around with you.

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Why do we have hair in our armpits then? (not trying to poke holes in this) i mean if what your saying is true then souldn't wea have also lost our armpit hair since it is almost continually in the shade?

 

Hairs like feathers are very versatile. In the case of armpits and genitals I think it is used for lubrication, while remaining an insulator on the head.

 

aguy2

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I believe sexual selection was at least partially the reason Homo Sapiens lost their hair.

 

A male who had less hair might have appeared more masculine, therefore being chosen by the opposite sex. As for females, the loss of hair would have made their breasts more exposed, leading once again to sexual selection. Now it is unlikely that individuals would lose hair on one place of the body (e.g.: breasts) but a certain mutation would make the individual overall less hairy.

 

There could have been a mutation in the either sex that favored hairless partners. The gene would be successful because the offspring would be more equipped to deal with bipedalism (Sweat theory as mentioned before in the post) and therefore pass the gene for "preferring hairlessness" down the generations.

 

One of the theories is that the reason we became bipedal in the first place is because our penises were more exposed to the opposite sex once we are standing up.

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The parasite idea is unlikely to be the reason. It would apply equally to apes and they still have hair.

 

Hair provides so much needed protection from the elements. It only became redundant after humans started wearing clothing.

 

Also, they are usually picking off salt crystals from each other - not ticks and fleas as is commonly thought.

 

Considering you're contradicting Richard Dawkins here, I'm going to go ahead and assume you're wrong.

 

Mokele? Care to chime in on that?

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Conversation between me and a snake

 

Me: why aren't you hairy , then?

 

Snake: Dunno really, I suppose if I was hairy, I would not be a snake. How about you?

 

Me: I suppose if all humans were hairy, how could you tell the difference between us and apes. But then even some of the bald ones act like apes. Sigh.

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I can't say how we lost our hair (surely what hair we have left is reminiscent of our ancient fur), but I can say why we have no hair. It was simply fate that took away our hair to force us to develop clothing. just as we have no claws or great strength or speed for hunting. so we are forced to develop weapons as fate intended. we are naturally the weakest creatures. so we create unnatural tools so that we may survive, all based on our natural instincts. the hair on our face and head do keep us warm. or at least it did at one point. and has now become as many of you are saying, a sexual preference.

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It was simply fate that took away our hair to force us to develop clothing.

 

I think the opposite assumption (i.e. development of clothes minimized the selection advantage of having hair; losing hair meant less time picking out parasites, more to spend on constructive activities, gathering food, etc) makes quite a bit more sense.

 

we are naturally the weakest creatures.

 

That's not true at all!

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