why is the lack of "fur" positive Progression for humans?

Hi, Arrogantape.

Welcome to EvC!

arrogantape writes: Although there really is no way to prove it, I believe we humans are the aquatic ape.

Although "prove" is a strong word, there actually are ways to provide evidence for your hypothesis.

First of all, evolution cannot work as a contingency plan. New features don't become fixed in populations "just in case." Natural selection can only push "plan A": that is, it works for things that are crucial, not for things that might be handy. That's why evolution tends to produce specialists.

So, since the genus Homo (and its pregenitors) appears to have arisen on the arid savannahs of Africa, you're going to have a very hard time explaining what selective pressures led to an aquatic lifestyle.

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arrogantape writes: Naked skin decreases swimming friction.

But, our heads, which presumably go first while swimming, still grow hair. If the loss of hair is for streamlining, shouldn't our head hair have been the first to go?

arrogantape writes: Adipose fat insulates, and smoothes. It also increases buoyancy.

Badgers and bats and possums have adipose fat too. Does this mean they are aquatic?

arrogantape writes: Babies instinctually know how to swim and hold their breath.

My baby doesn't.

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-Bluejay

Darwin loves you.

Hi, arrogantape.

arrogantape writes: It has been proven that all babies do instinctually know to hold their breath under water, and swim. Odd but true.

Care to throw your baby in the water to prove it?

On the website linked by Chiroptera earlier (Aquatic Ape), there is a page that addresses the reason why people think babies can swim. Basically, it is a misreading of an old (1939) scientific paper recording the behavior of mammals in water, which concludes that human infants move in the water in exactly the same manner as other young quadrupeds. Moore (the website guy) has this to say about it:

quote:

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So that's the sad secret of the drowning infants; what we actually find here is not so much "swimming babies" as infant mammals slowly drowning without a struggle.

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arrogantape writes: Our subcutaneous fat is plentiful compared to any other ape.

Also not true. Again, see the site Chiroptera linked for a refutation of this idea.

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Anyway, the topic of the thread is "fur/hair," not swimming or adipose tissue, so, let's talk about hair:

arrogantape writes: There is the ornamental side of head hair. We also have hair wherever it can gather body scent.

And this tells us that there are other factors that are more important in regards to hair than aquatic streamlining. You yourself have put "body odor" as more important than hydrodynamics.

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-Bluejay

Darwin loves you.

Hi, arrogantape.

arrogantape writes: Now, I'd say why on earth do our naked babies know how to swim, and love it, while no primate, other than the wading Japanese monkeys, have anything to do with water.

Did you even read the link, or even my comment in Message 68? Here's what you would have seen if you had:

quote:

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They always seem to mention the human infants and how their movements are usually "rhythmical and organized" and are "ordinarily sufficiently forceful to propel the baby a short distance through the water". So far so good. But they don't seem to ever mention the fact that the same study looked at other mammalian infants (opossum, rat, kitten, rabbit, guinea pig, and rhesus monkey) and found that they behaved the same way: "these rhythmical movements of the human infant are quite similar to those of other young quadrupeds in water".

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I guess it's my fault for not providing this particular quote in my message, but I did provide a link to it. The little commentary on Moore's site is really just a tiny blurb, so I thought it wouldn't be too much trouble.

Please note that another primate (rhesus monkey) was also tested in the same study and showed the same behaviors as human infants. So, please stop asserting that human infants are somehow unique in this ability without showing evidence that overturns my evidence.

And, maybe babies know how to hold their breath because they lived in an aquatic environment for the first nine months before parturition, and didn't breathe through their mouths during that time.

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arrogantape writes: It is hot where they live, yet they are well furred.

Most mammals from hot regions have fur: warthogs, lions, hunting dogs, anteaters, bats, bears, water buffalo, antelope, camels, zebras, capybaras, lemurs, tarsiers, etc. (The ones in bold are mammals with significantly thicker fur than primates.) Clearly, the presence of fur has nothing to do with climate.

Please also notice that elephants and rhinos and naked mole rats have lost their fur. None of these did so for hydrodynamic purposes.

arrogantape writes: There are nasty predators that stalk [bonobos], and so they still can use all limbs for running and climbing.

Australopithecus could probably outrun a bonobo, in terms of both absolute speed and endurance.
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By the way, if you put "qs=Person's Name" inside brackets [ ], then cut and paste the quote, then follow up with "/qs" in the same brackets, you get this:

Person's Name writes: This is a quote box.

You can push the "peek" button at the bottom of a message, and it will show you all the formatting and hyperlinking codes in that message.

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-Bluejay

Darwin loves you.

Hi, Ape.

arrogantape writes: Add to that our peculiar naked bodies, blubber floats, elongated body, AND a natural swimming instinct, and no wonder some of us question our origins.

Okay, here's a quote from the other link that I provided in Message 68:

quote:

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Morgan uses Pond's observations that humans are on the fat end of the scale compared to other mammals as her basis, but ignores Pond's observations that both quantity and amount of fat in humans is similar to that of captive monkeys if they aren't kept on a strict diet.

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So, there is nothing unique about human fat that point to a special adaptation to water. If you want to argue fat, you must understand that your argument also supports an aquatic origin for all mammal taxa.

Also, there is nothing unique about our natural swimming instincts, either.

So, what's left? Long legs and no hair.

These two are just as easily explained as a running adaptation as a swimming adaptation.

Also note that no truly aquatic mammal has long legs (you might could make a case for the capybara, but that's a bit of a stretch). In fact, no truly aquatic vertebrate, extant or fossil, has/had long legs. Every aquatic vertebrate has/had an elongated body and shortened hindlimbs, probably because long hindlimbs would increase drag.

arrogantape, message #73, writes: I ask everyone, what do you think this slender upright brachiate, Afarensis, have that made it so successful?

Free hands.

And better running ability than its forebears.

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-Bluejay

Darwin loves you.

Hi, Ape.

arrogantape writes: Sorry about my slowness to adapt to the posting styles here. I am a Macman and have an allergic reaction to codes.

:)

It was just some helpful information. It just makes the dicussion easier to follow.

Also, if you use the "Reply" button at the bottom of a message instead of the "Gen Reply" at the bottom of the page, the message appears as a response to that message, and lets people know who you're replying to. Some people are set up to receive E-mail notification when a response is written to them, and they don't get that notification if the response isn't attached to their message.

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arrogantape writes: I would not try to outrun a chimp or gorilla. I would loose.

I don't believe that chimpanzees and gorillas can outrun humans (on average, and assuming non-couch potato humans, of course).

I found one study, here, that puts maximum human running speeds at just under 8 body lengths per second, and gorillas at less than five and a half. Using the body lengths given in the study, that puts humans at around 24 mph, and gorillas around 20 mph.

Of course, they probably used an Olympic record for the maximum human speed (my university doesn't have a subscription to the paper where the numbers for this study came from, so I don't know), and average speeds would probably be more informative than maxima, anyway. However, I'm confident that the average human today is a poorer runner than our Paleolithic forebears.

arrogantape writes: Free hands are what the other primates have when they are not running, or climbing.

But, there would be an obvious survival advantage to being able to carry one's child while running.

arrogantape writes: I have stated, I cannot fathom how Lucy managed to survive.

Clearly, though, she did survive. I like to think Australopithecus could have waved its arms around while running to scare vultures off carcasses or even startle predators. Standing up makes you look bigger than you really are.

Of course, the topic is hairlessness in humans, and we seem to have gone quite noticeably off that topic. Perhaps we could open up a new thread about aquatic vs cursorial Australopithecus?

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-Bluejay

Darwin loves you.

Hi, Ape.

arrogantape writes: You know, I think we would agree on almost everything science wise. Too bad I started us on the wrong foot.

Don’t take anything I say personally (unless it’s obviously mean to be personal): you should know that scientists are all about beating up on each other’s theories. That’s the whole point. :)

I apologize if what I said was offensive to you.

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arrogantape writes: There is no refuting our physiology allows us to swim faster and far longer, as well as under water, than any other primate.

Well, there is also no refuting that our longer, skinnier fingers fit in smaller holes than a gorilla’s, but that doesn’t mean they were made for picking our noses.

Have you ever looked at a horse? I can only imagine that a primitive man, seeing how fast that horse can run, really wanted to know what it felt like to be moving that fast, and, seeing how long and flat that horse’s back was, thinking that that horse was just begging to be sat on anyway. There’s no doubting that the horse’s physiology is nearly perfect for use as a mount, but that doesn’t imply a causative link.

arrogantape writes: Our feet have nearly fully lost their prehensile ability, specializing in locomotion on land and in water.

I disagree: I don’t see how the human foot is specialized for locomotion in water. It doesn’t really look like the foot of anything that lives in water, as far as I can tell. In fact, I think it looks a lot more like the foot of a wolf or other cursorial mammal’s than an aquatic animal’s foot:

• The foot is elongated between the ball and the heel, allowing greater leverage in a running step. This is a trait common to felines, canines and theropods, but not seen in beavers, whales, platypuses, otters or seals.

• The toes are short, so they don’t break or make the step awkward (again, like the felines, canines and theropods, but not like aquatic mammals, which usually have long toes for walking in soft mud or for supporting a webbed foot).

Of course, our feet aren’t nearly as cursorially advanced as the canines’, felines’ or theropods’, but we had to compromise our running ability with our bipedal balancing ability, so that rather well explains the inconsistency there, I think.

arrogantape writes: I already mentioned all the changes our whole body has to go through to make bipedalism possible. There really is no workable intermediate. Unless...... that entails evolving to swim rather than walk first.

How would swimming bridge the gap between brachiating and walking upright? I don’t see any sort of connection here.

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-Bluejay

Darwin loves you.

Hi, Ape.

On the subject of "floodplains":

RAZD, message #86, writes: Curiously a flood plain is not always flooded, nor is seasonal flooding necessary to be classified as flood plain. The specification for heavily forested could easily be more descriptive of very occasionally flooded plains. Living in these kind if areas could just mean that the ground is easier to dig for finding tubers and that there are nut and fruit bearing trees and bushes growing in the fertile soil with a relatively high water table.

arrogantape writes: This was waterworld much of the year, if not always. Ramidus had to forage during the wet period.

You and RAZD have made counter-assertions. In this, RAZD has the advantage, because your argument relies on the term “floodplain,” and RAZD has shown that the term doesn’t always mean what you think it means. Now, one of you should present some evidence about the "floodplain" of eastern Africa ~5 Mya, because only case-specific evidence is going to resolve this issue.

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arrogantape, message #78, writes: I have stated, I cannot fathom how Lucy managed to survive... A slight naked upright gracile ape trotting about is lunch.

arrogantape writes: [In the water,] the big carnivores are not a threat, accept crocs, and they can be neutralized.

There’s an obvious disjunct here: Lucy is helpless on the plains, but she can neutralize crocodiles in the water? I don’t buy that at all.

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-Bluejay

Darwin loves you.

Hi, Ape.

arrogantape, message #94 writes: Anti aquatic story folks do not have a model of their own.

Yes, they do. They call it the "terrestrial ape hypothesis." Basically, it states that the hip and pelvic structure are adapted for walking on the ground.

A specific flavor of this model (with a couple variations) has been presented in this very thread: free hands while walking (for carrying food or young or for brandishing sticks or scaring predators).

There is also the tree-walking hypothesis: bipedal, upright locomotion actually evolved for walking along tree branches (this is obseved in orangutans), and was thus a "preadaptation" for terrestrial locomotion.

arrogantape writes: ...by suggesting a crocodile can be more easily neutralized than leopards, lions, and hyenas, is simply because it is only one type of carnivore to keep an eye on, and learn it's habits. By hanging in trees over water, the whereabouts of crocs would be known.

I thought hanging in trees was ruled out in the bipedal creatures by both the terrestrial and aquatic ape hypotheses.

arrogantape writes: I really don't think they would live near [crocodiles] anyway.

I don't think this is a viable idea: if you're living near the water, you're living near crocodiles. The crocodiles will generally go wherever you go if they want to eat you.

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I think you've misunderstood some of what the aquatic ape hypothesis says. It doesn't say anything about swimming or aquatic locomotion, just that upright walking was originally used for wading. Like RAZD, I won't say that our ancestors didn't wade, but I will say that it was not the underlying mechanism of hominid evolution: we are not adapted to a true aquatic lifestyle. Swimming adaptations are not posited by the aquatic ape hypothesis, and are not upheld by the evidence, anyway.

Remember the foot argument I made in Message 90?:

arrogantape writes: The foot is elongated between the ball and the heel, allowing greater leverage in a running step. This is a trait common to felines, canines and theropods, but not seen in beavers, whales, platypuses, otters or seals. The toes are short, so they don’t break or make the step awkward (again, like the felines, canines and theropods, but not like aquatic mammals, which usually have long toes for walking in soft mud or for supporting a webbed foot).

This is clear evidence of a cursorial history, and is very difficult to rationalize with a wading or swimming history, even though I have found proof here that chimpanzees wade.

arrogantape, message #103, writes: I bet tool making started with the crushing of clams with rocks.

I bet not.

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-Bluejay

Darwin loves you.

Hi, Ape.

Welcome back. It’s good to see you(r words) again.

I have not spent much time thinking about the Aquatic Ape Hypothesis since you last left us, but your return has prompted me to think about it a little bit more. I am not so antagonistic to it as I was before (though I still reject it at the current time).

First off, even though the flat foot is off-topic for this thread, I wanted to mention it peripherally. Only Homo floresiensis has flat feet among the genus Homo: can this really be seen as anything more than evidence that the hobbit was aquatic? How does it suggest that our ancestors were aquatic, when the adaptation appears after the emergence of our species?

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But, to get back on the topic of nakedness, I don't understand why nakedness points to an aquatic origin. The only naked aquatic mammals are cetaceans: all other aquatic and semi-aquatic mammals have fur.

It seems that, in every case, mammals adapting to an aquatic lifestyle developed webbed toes, flippers, blubber, and/or closable nostrils before they lost their fur.

For example, consider the following: beavers and muskrats, otters, seals, the water opossum and even the platypus. All of these are semi-aquatic or aquatic mammals, yet all of them still have their fur. Is there a reason for hypothesizing that aquatic apes are an exception to this trend?

It seems that, if hairlessness in apes is to be explained as an aquatic adaptation, the lack of flippers, blubber, and closeable nostrils would all be found wanting an explanation. Thus, wouldn’t it be more parsimonious to explain the lack of fur as a way to shed heat on the savannah?

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

RAZD writes: So how did this dimorphism evolve if aquatic adaptation is the cause for loss of terminal hair? If you use aquatic adaptation to explain the evidence of smoother appearing skin, then you must explain the dimorphism, or you have explained one sex and not the other.

Looking at this from a genetics perspective, I don't think this statement is accurate. According to Wikipedia, sexual dimorphism in body hair pattern is due to the activity of androgens, which produce more body hair in males.

If Wikipedia is correct, then there seems to be at least two different genetic mechanisms at work, one that explains the sexual dimorphism, and one that explains the difference between us and the other apes.

These two mechanisms need not even be linked at all. So, I don't think Ape actually has to explain the dimorphism in order to explain the "hairlessness."

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

RAZD writes: It explains how the specific dimorphic pattern occurs, but not why it occurs.

It shows a mechanistic distinction between dimorphism and "hairlessness." Whether or not the two mechanisms are linked is now the question that should be addressed.

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RAZD writes: From the continued degree of variation within the population it is evident that there is no strong selection pressure one way or the other on male hair patterns.

This would be true, no matter what the original cause was. There is currently no strong selection pressure on thermoregulatory ability or swimming ability, either, which is equally compatible with the existing variation in hair pattern.

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RAZD writes: There is still active selection of less body hair in females, however now it is achieved with tools instead of genes.

This could get into a chicken-and-egg scenario: we could just as easily have become "naked" first by some other mechanism, and only afterwards have associated "nakedness" with female sexuality because of the differences due to hormone activity.

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RAZD writes: The question is still why that particular genetic adaptation was selected for, rather than one that would provide universal and equal loss of terminal hair.

How can I answer the question, "Why didn't X happen?"

Why didn't snakes on the African savannahs develop rattles to warn ungulates not to step on them, as snakes in North America did?

However, since the development of terminal hairs seems to be tied to male hormones, total nakedness would seem to incur reproductive costs on males. Thus, the existing pattern may be a compromise between thermoregulation and hormonal requirements for reproduction.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

RAZD writes: That doesn't explain the existence of males with hair similar to females, and they appear to be rather robustly represented in the population.

And females that are hairier than I am are also fairly common in the population.

Over 170 genes are involved in hair morphogenesis(according to this abstract, anyway): you can't expect there to not be noise.

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RAZD writes: If reproduction is not hindered, then the androgen theory fails to explain why the apparent hairlessness of males and females is different.

Except that, curiously enough, the difference is known to be caused by androgens. That's why "androgenic hair" is the technical term for the hair that men grow and women don't.

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I have nothing against a sexual selection explanation for hairlessness, but the simple observation is that there are two factors involved: one makes all humans "hairless," and another makes males grow extra hair.

So, there is some mutation that causes both sexes to be equally hairless, which is what you've been asking Drew to produce. But, there is a second genetic mechanism involved, which is a side effect of male hormones. This second mechanism is acted upon by sexual selection. But, this does nothing to show what the first mechanism was for.

In fact, it is consistent with all three hypotheses so far proposed. The aquatic ape hypothesis is faulty for other reasons, but the thermoregulatory hypothesis is still intact.

I am not advocating any one of these models, but I think it should be acknowledged that the dimorphism and the "hairlessness" are not necessarily the same question, and no evidence so far presented is able to link them. Your evidence still has not explained the first mechanism.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

RAZD writes: Bluejay writes: Over 170 genes are involved in hair morphogenesis(according to this abstract, anyway): you can't expect there to not be noise. So any one of them could have been used to produce the effect of bare skin rather than the one that was chosen by selection. Any one of them could have been used to promote universal bare skin, if that is what the driving selection mechanism was finding beneficial. That none of them were actually selected to produce bare skin, leads to the logical conclusion that bare skin was not the desired result.

Lots of things could have been, but aren’t. You can’t make an argument about evolution from what didn’t happen unless you accept teleology as a valid explanatory framework.

The fact is that one mutation did happen, and it would have worked well enough: there’s no reason to think that something else should have happened. You don’t need bare skin to improve the efficiency of perspirative cooling over hairy skin.

Besides, I can turn it back on you: If the fact that we’re not completely bare disproves the evaporative cooling hypothesis, then how does the fact that men are generally less attracted to 12-year-olds than to 20-year-olds not disprove sexual selection for younger-looking females?

You don’t have to take everything to the extreme to make it work.

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RAZD writes: But male bareness has not been selected for, as there are plenty of phenotypes available to produce the effect while hairy patterns are still evident in the population, nor do we see any continued selection effect for bareness in males the way we do in females.

If you take away a male's ability to produce or respond to androgens (testosterone specifically, I think), you get a male (usually underdeveloped and feminized) with female pattern body hair (here is Wikipedia on the subject). So, the dimorphism in hair pattern is due to a hormonal mechanism. That the non-androgenic pattern of body hair in humans is different from the typical pattern for other apes shows that something else (independent of androgenic dimorphism) caused our hair’s development to be arrested before the terminal stage.

It might be sexual selection for younger-looking females that is secondarily inherited by males.
It might be natural selection for increased efficiency in perspirative cooling.

The obvious answer is that the dimorphism does not need to be explained by whatever this mechanism turns out to be, because the dimorphism already has an independent explanation that can very readily and easily be observed.

So, you need to produce evidence other than dimorphism to show that our relatively underdeveloped hair is due to sexual selection.

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That males have no stabilizing selection for a specific amount of body hair is also meaningless, because we haven’t lived on the savannahs for a long time. However, I would like to point out that there is a difference in mean hairiness between African and Caucasian men, which is consistent with the savannah hypothesis.

It could indicate that Caucasians started growing more hair after they went to Europe, or that there was continued selection in Africa for males to be less hairy (either sexual or natural selection may be the case). But, whatever the case, it is not explained by sexual dimorphism.

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RAZD writes: The "Savannah" theory can be ruled out because it doesn't explain features that evolved before the Savannah ecology.

What features evolved before the savannah ecology?
And, what do these features have to do with the loss of terminal hair in humans?

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RAZD writes: Hair loss in other cursorial hunters in the same environment does not occur (see dogs), so it is contradicted by other evidence.

Why doesn’t the observation that dogs, hyenas and cats don’t sweat fully explain the disparity?

Homo is the only alleged cursorial hunter on the savannah that uses evaporative cooling as a major thermoregulatory mechanism on its entire body, and thus, is the only cursorial hunter who stands to gain thermoregulatory advantages from losing its terminal hair.

The appeal to other cursorial hunters as negative evidence fails.

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RAZD writes: Ok, then add this up: • No loss in the number of hairs in either males or females. This rules out any selection for loss of hair. ::Not explained by aquatic adaptation. • What is selected is arrested development of hair at a juvenile pattern, similar to many other features selected (see neoteny above). ::Not explained by aquatic adaptation. • Terminal hair on female legs is still part of the modern pattern of hair development. This is the part most in the water, the part under high drag when kicking during swimming -- ie this pattern in women is not consistent with the aquatic adaptation conjecture (while none of the male pattern is consistent with the aquatic ape conjecture). ::Not explained by aquatic adaptation. • Selection for younger and barer appearing women is still very active in our population, as would be expected for a run-away sexual selection mechanism.} ::Not explained by aquatic adaptation. • Humans living in coastal ecologies since prehistoric times show no additional adaptation nor retention of any feature that is of benefit to living in that ecology compared to Tibetans as a control. ::Not explained by aquatic adaptation.

You’re talking to Bluejay now, not Arrogantape: I have already rejected the aquatic ape hypothesis.

Note also: I acknowledge that there is no loss in the number of hair follicles. However, I will continue to use the terms “hairless,” “bald” and “hair loss” (always in quotation marks) to refer to the defecit of terminal hair, because “underdeveloped hair” and “arrested development of terminal hair” make very awkward sentences. But, know that this is not a point of contention between us.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

Sorry I'm taking so long on this. I'm trying to get a reply together, but it's turning out to be a lot more work than I really want to put in to EvC, and my field work is starting to pick up now that the rain is gone.

But, I'll have some stuff to present soon (probably not nearly as spectacular as I want it to be, though).

Thanks.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.

Hi, RAZD.

Sorry I took so long on this: it took me this long to solidify my thoughts.

Here is my argument against sexual selection as the mechanism for hairlessness in humans:

Human males do not have a random distribution of body hair patterns. Asian males are predominantly “hairless,” and Caucasian males are predominantly hairy. African males are intermediate, having both hirsute and bare patterns. This 1960’s study has the hairiest and barest chest hair patterns being the two most common groups in African American men, creating a bimodal pattern, which could suggest disruptive selection, in which both hairiness and bareness are selected for.

Interestingly, when you look even closer, you see a different picture. The earliest living branches of humanity, the Khoisan and Pygmies, have very bare-chested males (Google "Khoisan people" or "pygmies" and count how many hairy-chested males you see: none of them wear shirts, so it's easy to tell), and it’s actually the later-branching groups that account for the hairiness in African males. This implies that bareness is the initial condition for male Homo sapiens, and that hairiness in males is atavistic. Thus, the atavistic hairiness of males explains the dimorphism, not the hairlessness of females.

Thus, while sexual selection for bare skin seems to be prevalent today, and may very well be the cause of sexually dimorphic hair patterns in Caucasians, it couldn’t possibly have been the primal cause, because early Homo sapiens were not sexually dimorphic in terms of body hair patterns.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.