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Author Topic:   why is the lack of "fur" positive Progression for humans?
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 156 of 202 (509450)
05-21-2009 9:59 PM
Reply to: Message 155 by arrogantape
05-21-2009 10:10 AM


Re: woodland forest apes and bareness selection
Hi arrogantape
What answer do you want from me on sexual dimorphism? Yes, it exists. If you are alluding to modern male and female differences, yes, indeed, there are remarkable differences. The female of our species is smoother skinned.
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 dimporphism, or you have explained one sex and not the other.
You are assuming our species is the end product of a steady progression.
Not at all, just that there is a survival or reproductive benefit to the adaptation of new traits.
We could have inherited the naked trait, and the bipedal mode of moving about, plus tool making from our distant semi aquatic ancestors.
There is no evidence of any semi-aquatic ancestors. There is evidence of woodland jungle apes and Savannah apes. There is no evidence of tools developed to use in a marine environment. There is evidence of tools developed to use in a Savannah environment and one mixed with pockets or woodland jungle.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 155 by arrogantape, posted 05-21-2009 10:10 AM arrogantape has replied

Replies to this message:
 Message 157 by arrogantape, posted 05-22-2009 12:35 PM RAZD has seen this message but not replied
 Message 158 by Blue Jay, posted 05-22-2009 5:22 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 159 of 202 (509601)
05-22-2009 5:59 PM
Reply to: Message 158 by Blue Jay
05-22-2009 5:22 PM


Re: woodland forest apes and bareness selection
Hi Bluejay
If Wikipedia is correct, then ...
It explains how the specific dimorphic pattern occurs, but not why it occurs.
There is still plenty of variation in body hair in males, that active selection for less body hair phenotypes to operate in the population, and then those males would be preferentially selected for. There is still plenty of variation in body hair in males, that active selection against particularly hairy male phenotypes to operate in the population, and then those males would be preferentially selected against. 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.
There is still active selection of less body hair in females, however now it is achieved with tools instead of genes.
http://www.visit4info.com/...Womens-Razors-Blades-Range/3298
Obviously this sexual selection is still going on. Interestingly, several experiments have shown that one of the markers of run-away sexual selection is that a trait is driven to one end of the spectrum, and that artificially enhanced specimens that are made outside of what is possible within a population, will be actively sought for mating.
Curiously, the main areas where women shave these days includes their legs, where female terminal hairs normally grow, and which would be most effected by an aquatic adaptation.
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."
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.
Enjoy.
ps - buy stock in razor companies ... and shave your losses ...
Edited by RAZD, : clrty
Edited by RAZD, : gleshin

we are limited in our ability to understand
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Rebel American Zen Deist
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This message is a reply to:
 Message 158 by Blue Jay, posted 05-22-2009 5:22 PM Blue Jay has replied

Replies to this message:
 Message 161 by Blue Jay, posted 05-22-2009 6:35 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 163 of 202 (509615)
05-22-2009 9:34 PM
Reply to: Message 161 by Blue Jay
05-22-2009 6:35 PM


Re: woodland forest apes and bareness selection
Hi Bluejay,
However, since the development of terminal hairs seems to be tied to male hormones, total nakedness would seem to incur reproductive costs on males.
That doesn't explain the existence of males with hair similar to females, and they appear to be rather robustly represented in the population. Thus it would appear that the reduction of hair on males is not a hindrance to reproduction. It also does not seem to be undesirable: google male models.
If reproduction is not hindered, then the androgen theory fails to explain why the apparent hairlessness of males and females is different.
Female "bareness" is consistent in 99.9% of the female population in a highly skewed distribution.
Male "bareness is variable from one end to the other and has a relatively "normal" distribution in the population.
One distribution indicates selection, the other does not. It is the distribution of the traits in the population that shows that female bareness is a result of selection. The variation seen in males is due to secondary effects of the selection in females, effects that have neither positive nor negative consequences for reproductive success.
Enjoy

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 161 by Blue Jay, posted 05-22-2009 6:35 PM Blue Jay has replied

Replies to this message:
 Message 166 by Blue Jay, posted 05-23-2009 11:38 AM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 175 of 202 (509755)
05-24-2009 11:45 AM
Reply to: Message 166 by Blue Jay
05-23-2009 11:38 AM


Re: woodland forest apes and bareness selection
Hi Bluejay,
As Jon (Message 164) has pointed out, the sexual selection was for young appearing females, rather than hairlessness per se, the logical result is that selection is NOT for bare, just the hair pattern of children in females, which explains the retention of vellus hair on females as well as on males, while the terminal hairs are selected against in females but not in males.
We have other evidence of the selection for youthful appearance as neoteny also explains the retention of the youthful face shape in humans, the face shape you see in young chimpanzees and gorillas, and to a lesser extent in the older hominids.
Studies have shown that this desire for youthful appearing female mates is still strong today, so we have evidence of an active mechanism, we have evidence of how that mechanism operates, and we don't need to propose some additional mechanism, especially an additional mechanism that is at variance with the fossil evidence AND at variance with the existing pattern of hair development.
See Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution thread again (message 1):
quote:
This is observed in many species, and in humans there are several theories on the issue of "beauty" but one of the consistent factors involved is that the more beautiful faces are averaged (see average face-ness: click) -- more on this in humans later.
...
The question can also be investigated by what is considered beautiful (women) or handsome (men) and does it show a skewed pattern. This goes back to the average face issue raised above: "average face-ness" was not enough to fully explain the whole pattern in the experiment as there was also a clear bias in the data for youth (see babyface-ness: click), and the summary comments on this include these statements (read Summary: click for the whole summary):
(1) The results of our study are quite surprising. Compound (i.e. morphed) faces were, on average, regarded as being more attractive than the original faces. ...
(2) For female faces, it could be shown that babyface attributes - such as large, round eyes, a large domed forehead and small, short nose and chin lead to a rise in attractiveness values.
(3) To sum up, our study shows clearly that the most attractive faces do not exist in reality, they are morphs, i.e. computer-created compound images you would never find in everyday live. These virtual faces showed characteristics that are unreachable for average human beings.
They also found "averaged" but not "babyfaced" beauty applied to males and thus it looks like human beauty involves both and (average individual icon} for many features and a skewed {extreme individual icon} tending towards idealized younger looking sexually mature females. That this also demonstrates the same pattern of run-away sexual selection noted for breasts, buttocks and bareness is not likely to be an accident.
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.
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.
Which causes the "desired" result - younger appearing women that have still retained juvenile pattern hair. As noted before, arrested development is a common result in many species, when reproductive ability is reached before a feature is fully formed. This too is logical, as then the energy is put into reproduction rather than further development of the already reproductively successful organism.
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.
Males do not grow extra hair, they have retained more of what would be normal hair if selection for female appearance were not involved. The male patterns of hair is due to combination of non-selection in males (so retained hair features are selected out) and cross-over effects where males inherit the result of selection in females.
So, there is some mutation that causes both sexes to be equally hairless, which is what you've been asking Drew to produce.
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.
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.
No, there is one selection force acting on a number of genes, with positive result in females and non-relational results for males.
In fact, it is consistent with all three hypotheses so far proposed.
Only one of which explains all the evidence. The "Savannah" theory can be ruled out because it doesn't explain features that evolved before the Savannah ecology. Hair loss in other cursorial hunters in the same environment does not occur (see dogs), so it is contradicted by other evidence.
Similar for the aquatic ape theory: it is contradicted by sexual dimorphism in hair patterns.
The aquatic ape hypothesis is faulty for other reasons, but the thermoregulatory hypothesis is still intact.
One other reason being a complete absence of any supporting evidence.
But it is not a thermoregulatory hypothesis, it trys to explain the loss of a thermoregulatory feature. That seals and otters are perfectly capable of thermoregulation with full fur shows that this argument does not explain the retention of fur in these organisms.
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.
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.
Sexual selection explains all the evidence, it is consistent with the fossil evidence, it is consistent with the hair patterns in chimpanzees and gorillas, especially while breast-feeding.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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This message is a reply to:
 Message 166 by Blue Jay, posted 05-23-2009 11:38 AM Blue Jay has replied

Replies to this message:
 Message 176 by Blue Jay, posted 05-25-2009 12:09 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 177 of 202 (509867)
05-25-2009 4:21 PM
Reply to: Message 176 by Blue Jay
05-25-2009 12:09 PM


Re: woodland forest apes and bareness selection
Hi again Bluejay,
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.
Agreed. It's the old forensic question/s of "means, motive and opportunity" to figure out what most likely occurred in the past.
We could say that the means is genetic mutations, the motive is natural selection for increased ability to survive and reproduce, and the opportunity is an ecology where the changes can take effect (or we could say that the mutations provide the opportunity, natural selection provides the means, and the ecology provides the motivating force - your pick). We also need to explain all the evidence, not just what happened, but the timeline for when it happened.
You don’t need bare skin to improve the efficiency of perspirative cooling over hairy skin.
Which does not explain why horses sweat (profusely) and yet there are no bare horses I am aware of. Thus perspiration does not explain the arrested development of hair, nor does it explain why females would be more affected than males.
Instead we see that ecrine glands are already existing on the chests of other apes, and thus are most likely to exist on out common ancestors -- ie the ability to sweat pre-dates the division of humans from chimpanzees and gorillas, although at that stage it was used to keep bare-ish skin soft and supple, as in on breasts during feeding (as seen in chimps and gorillas).
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?
Pedophiles and child pornography do show that some men are much more attracted to 12-year-olds than to 20-year-olds. You also have many cultures where marriages take place with 12-year-old women and old(er) men.
The fact remains that IF cursorial hunting and the sweating ability of the hunter causes selection for bare skin, that then the barer sex should be the one doing the hunting.
You don’t have to take everything to the extreme to make it work.
I'm not taking it to the extreme, rather I'm looking at the evidence that selection has gone to one extreme end in hair development in women, and I note that this is one of the signs of runaway sexual selection. Then I note that this pattern is not extreme in men.
Don't you agree that a species with a more advanced selected feature would the one more affected by selection process?
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.
If you block the males ability to produce testosterone altogether the default pattern of development is female, complete with fully formed female genitalia and breasts (just no fallopian tubes or ovaries). So if you block normal male development, you are left with development inherited via the X gene from females.
Curiously this "default" pattern of development includes the female hair patterns as have been selected in females, and thus - again - showing that the selection occurred in the female genes and that any effect on males is what they inherit from the selection in females.
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.
So then why are the running sweating hunters less affected by this selection than the non-running non-hunting gatherers and protectors of children? This is why the Savannah fails to explain the evidence: the selection should be more extreme in the males and it isn't.
Males are probably significantly less effective at cooling than females, due to body mass to surface skin ratios, while at the same time exercising more?
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.
But not with Tibetans, who have less hair than Africans.
What features evolved before the savannah ecology?
Bipedal gait is one that is now generally accepted to pre-date the Savannah theory. This used to be the major argument for the theory.
The existence of bare skin in other closely related apes means that the common ancestor likely had bare skin areas, particularly on the chest, and especially on the female breasts. Thus this likely predates the split of humans and chimps and gorillas.
These bare areas are kept soft and supple through moisture from the ecrine glands that cover the chests of these apes, but not of older common ancestor apes, where they are limited to hands and some other specific areas. These same glands are what are now developed on humans to cover more areas and used for one form of thermoregulation via sweat.
Thus both bipedal gait and some bare skin areas protected by proto-sweat glands pre-date the Savannah. This gave the upright barechested hominid a pre-adapted advantage when the Savannah ecology arose: it could extend it's territory into the open patches and still survive happily in the wooded jungle groves -- where, not incidentally, fossil evidence places them.
Cursorial hunting does not require, nor necessarily benefits from, replacing fur with arrested hair development.
Sweating horses do not require, nor would they necessarily benefit from, loss of hair (would a completely shaved horse run faster or longer?)
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.
So why don't horses, that sweat, lose their hair in order to survive being caught by wolves, cursorial hunters with fur? If it was a superior method or a survival benefit of any kind, then why are there NO bare horses, while horses that have bare spots are considered diseased? Why aren't racing horses shaved?
http://answers.yahoo.com/question/index?qid=2009011114494...
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.
And "apparent bareness" is also awkward. Nonvisible hair?
Question: why do "blonds have more fun" -- how do blonds evolve in a cursorial hunting or aquatic ape or sexual selection model?
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 176 by Blue Jay, posted 05-25-2009 12:09 PM Blue Jay has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 178 of 202 (510125)
05-27-2009 10:30 PM
Reply to: Message 176 by Blue Jay
05-25-2009 12:09 PM


Sequential evolution rather than multiple at once features
Hi Bluejay,
Just adding another element to the discussion: timing.
To me the major problem with the Savannah Theory is timing - several things have to evolve at the same time for it to work: the bareness plus sweating to regulate heat during the day to prevent hyperthermia and the subcutaneous fat layer to regulate heat during the night to prevent hypothermia. And it has to be done in a short period of time, as the evidence shows hominids expanding with the Savannah.
Much easier to envisage evolution of bare areas as sexual signalling, this being enhanced by upright posture, and the expansion of ecrine glands in the increasing bare areas. The wooded forest and the pre-Savannah climate means that the nights are not cool enough to need the warmth of the subcutaneous fat layer, and this evolves later after the bareness has expanded to the point where it is needed, and as the climate changes. Then the ecrine glands become more versatile as sweat glands when the hominids move into the Savannah, pre-adapted to take advantage of the opportunity.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 176 by Blue Jay, posted 05-25-2009 12:09 PM Blue Jay has replied

Replies to this message:
 Message 179 by Blue Jay, posted 05-28-2009 12:57 PM RAZD has seen this message but not replied
 Message 180 by Blue Jay, posted 05-31-2009 11:14 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 181 of 202 (510946)
06-04-2009 10:59 PM
Reply to: Message 180 by Blue Jay
05-31-2009 11:14 PM


Re: Sequential evolution rather than multiple at once features
Thanks Bluejay, I hope my delayed response is not too late.
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.
Interesting. However, I have several problems here, not least of which is that I have not said there is no effect on males.
First, where there is more disadvantage to the loss of hair I would expect survival selection of atavistic growth to occur, except where it was suppressed by continued selection. If sexual selection was recent comparatively then there should also be some groups with more than average atavistic women, and I would expect those groups to correlate with male atavistic growth -- if the selection for a return to heavier hair growth was an advantage. I would expect this in Tibet and the pole areas.
Second, curiously, I would expect the earliest living branches to show the most complete development of less visible hair, especially in an environment where it was not a significant disadvantage. I would expect to see the most compensatory systems to counter the disadvantages of less visible hair, and thus I would also expect to see the most cross-over of effects from selection in one sex to the other in a trait that is not sex-linked. Without any selection pro or con on hair visibility in men I would expect that over time they would tend to become less visible as well, just because of the shared genes. Thus every mutation that promoted less visible hair in females would be selected, and the male offspring would inherit all the mutations not bound to sexual differentiation. Remember, that while they may represent an old lineage, this does not mean that they have not continued to evolve from a common ancestor population, so this muddies the picture.
Third, I would also expect the same pattern in other "earliest living branches" and a correlation to the divergence of human population as it spread across the globe for consistency.
http://news.nationalgeographic.com/...13_journeyofman_2.html
quote:
Wells says his evidence based on DNA in the Y-chromosome indicates that the exodus began between 60,000 and 50,000 years ago.
In his view, the early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migration out of Africa.
...
Many archaeologists, however, believe that Australia, the Middle East, India, and China were inhabited much earlier.
"The dates don't compare well to the order or the geography of the migration patterns revealed by the fossil record," said Brooks. "Y-chromosome data give consistently younger dates than other types of genetic data, such as mitochondrial DNA."
A map from http://freepages.genealogy.rootsweb.ancestr.../...oChart.htm
So Australian Aboriginals would be a check on this hypothesis, as with a similar genetic age and environment, they too should be among those with less visible hair.
Not very hairy chested, but lots of male facial hair, and the males have more visible back hair.
NCBI
Overall more visible male hair than Asians?
In modern humans facial hair seems to be sex linked, so the retention of facial hair in males would mean these are the areas not subject to cross-over of selection for less visible hair in females.
2008 | Mathilda's Anthropology Blog. | Page 21
quote:
Correspondence analysis shows that three main clusters of populations can be identified: northern, eastern, and sub-Saharan Africans. Among the latter, the Khoisan, the Pygmies, and the northern Cameroonians are clearly distinct from a tight cluster formed by the Niger-Congo-speaking populations from western, central western, and southern Africa. Phylogeographic analyses suggest that a large component of the present Khoisan gene pool is eastern African in origin and that Asia was the source of a back migration to sub-Saharan Africa.
(bold in the original)
See J1J2 in N.Africa on the map above for Asian back migration. Also see the link between East Africa CR and Australian Aboriginal C. Unfortunately I can't tell what group(s) would the the Khoisan.
And at the end of the day, there is still sexual dimorphism in these groups, and men have hair where women don't, even if it is only facial hair, and they still show more variation in degree of hair visibility.
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.
They also would not have the benefit of further selection in the original ecology for other mutations causing less visible hair, especially where it becomes more critical to survival -- remember one of the markers of run-away sexual selection is that it drives the selection trait to an extreme condition: it is not possible for females to gain less visible hair without actual loss of hair follicles.
So I don't think your conclusion is valid: there is still sexual hair dimorphism in these populations, and there is no question of sexual selection today. Thus on one hand we have an existing selection pattern and an overall result consistent with it, on the other you have some other unknown selection process, but still have sexual selection today.
And you still have the problem of timing, to derive apparent bareness, the growth of subcutaneous fat and the derivation of sweating from ecrine glands, in a logical pattern consistent with the fossil record and the paleo-climates.
Enjoy.
Edited by RAZD, : stiles problem
Edited by RAZD, : clrty
Edited by RAZD, : tibet again
Edited by RAZD, : rev

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 180 by Blue Jay, posted 05-31-2009 11:14 PM Blue Jay has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 183 of 202 (511915)
06-12-2009 6:16 PM
Reply to: Message 182 by cervical
06-12-2009 3:58 PM


clothes make the man?
Hi cervical, and welcome to the fray.
There are obvious reasons for hair in nature. Is there a reason for hair when you have established a means of creating shelter? What if we lost our hair simply because the hairyness no longer gave an advantage?
There are lots of animals that build shelters to increase their survival ability, so this would not be a new thing, however one should consider the timing of the hair loss to the ability to build shelters and the needs for shelter at the time (and climate) where the individuals lived.
There is also the issue of clothes and pests.
http://www.newscientist.com/article/dn3807
quote:
Humans may have lost their body hair to reduce their vulnerability to fur-loving parasites and therefore attract the opposite sex, a new evolutionary theory proposes.
...
A widely accepted view is that humans lost their hair to help control their body temperature as they evolved into upright creatures on the warm plains of the African savannah. But this theory has problems that researchers believe the new theory can solve.
...
However, if humans evolved to beat parasites by losing the hair they hide in, why did our hirsute ape cousins not do the same? The reason, says Pagel, is that we also developed our own culture. We are the only ones who learned to build fires and shelter and to make clothes, he says, all of which helped us keep warm while shedding our fur.
...
Pagel says natural selection might initially favour less hairy individuals, as they have fewer parasites. But sexual selection could accelerate the loss of fur, as more naked early humans could be fitter and therefore more attractive as mates.
Clothes, however, would also provide an environment for pests, and there is still the massive (more than on any other ape) head hair to provide continued opportunity for the parasites.
My personal opinion is that it was due to sexual selection, selection which is also evident in neoteny and long head hair (think long tail feathers for a similar selection feature).
I also believe (again personal opinion) that it was well underway before man ventured onto the Savannah, as we see similar patterns of bareness in Gorillas and in Chimps, just to a lesser degree, but this indicates bareness was an existing feature in the common ancestor ape population. We also share a distribution of ecrine glands on the chest that other apes do not have. In chimps and gorillas these glands keep the bare skin areas moist and supple, and it is these glands that became the sweat glands in humans.
The climate in the woodland forest ecology before the Savannah was temperate and buffered from day\night variations by the forest, thus this would enable apparent bareness without endangering survival, something the Savannah cannot do.
Enjoy.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 187 of 202 (533797)
11-02-2009 10:29 PM
Reply to: Message 186 by arrogantape
11-02-2009 5:01 PM


No Predators?
Let's put one of your wild assertions to bed, arrogant ape:
Flores was unnatural as it had no large predators.
Flores - Wikipedia
quote:
Flores is one of the Lesser Sunda Islands, an island arc with an estimated area of 14,300 km extending east from the Java island of Indonesia. The population is estimated to be around 1.5 million [2], and the largest town is Maumere.
Flores is located east of Sumbawa and Komodo and west of Lembata and the Alor Archipelago. To the southeast is Timor. To the south, across the Sumba strait, is Sumba and to the north, beyond the Flores Sea, is Sulawesi.
The west coast of Flores is one of the few places, aside from the island of Komodo itself, where the Komodo dragon can be found in the wild. The Flores Giant Rat is also endemic to the Island.
In September 2003, at Liang Bua Cave in western Flores, paleoanthropologists discovered small skeletons that they described as a previously unknown hominid species, Homo floresiensis.
Komodo Dragons are scavanger predators, fully capable of taking down full sized humans, they can be fast, and they are dangerous ambush predators.
Komodo dragon - Wikipedia
quote:
The Komodo dragon (Varanus komodoensis) is a species of lizard that inhabits the islands of Komodo, Rinca, Flores, and Gili Motang in Indonesia.[3] A member of the monitor lizard family (Varanidae), it is the largest living species of lizard, growing to an average length of 2 to 3 metres (6.6 to 9.8 ft) and weighing around 70 kilograms (150 lb). Their unusual size is attributed to island gigantism, since there are no other carnivorous animals to fill the niche on the islands where they live; their large size is also explained by the Komodo dragon's low metabolic rate.[4][5] As a result of their size, these lizards dominate the ecosystems in which they live.[6] Although Komodo dragons eat mostly carrion, they will also hunt and ambush prey including invertebrates, birds, and mammals.
...
The evolutionary development of the Komodo dragon started with the Varanus genus, which originated in Asia about 40 million years ago and migrated to Australia. Around 15 million years ago, a collision between Australia and Southeast Asia allowed the varanids to move into what is now the Indonesian archipelago, extending their range as far east as the island of Timor. The Komodo dragon was believed to have differentiated from its Australian ancestors 4 million years ago. However, recent fossil evidence from Queensland suggests that the Komodo dragon evolved in Australia before spreading to Indonesia.[10] Dramatic lowering of sea level during the last glacial period uncovered extensive stretches of continental shelf that the Komodo dragon colonized, becoming isolated in their present island range as sea levels rose afterwards.[9]
So they were on the island before H.floresiensis.
There is also some evidence that humans (including H.erectus aka Javaman) also used the lowered sea level to walk to many places that are now islands.
Enjoy.

we are limited in our ability to understand
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 189 of 202 (561485)
05-20-2010 8:51 PM


Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Exchange with Mr Jack from Message 49 to Message 52 on Is body hair a functionless vestige? moved here:
quote:
RAZD Message 48:
Hi Coyote,
My guess on this is that the selection pressure was to remove hair to promote cooling.
(1) There has been no removal of hair - the apparent bareness is due to hair being arrested in an immature stage, vellus hairs, common on juveniles before puberty.
One old idea was that this may have been needed for persistence hunting, where people simply ran their prey to exhaustion.
(2) IF this were true THEN the most hairless appearing humans would be the hunters and not the gatherers. Conclusion: women did the hunting while the men did the gathering. Please compare this to what you know about anthropology.
(3) This also explains why other cursorial hunters, like wild dogs and wolves, are naked ... ?
If this is the case, the selection pressure to reduce hair would work up to the point where it didn't matter much any more; the selection pressure would end when the cooling was just good enough.
(4) OR the selection pressure would prevent total loss of hair when it reaches levels that endanger survival of the organisms, because the nights are a considerably different temperature, to say nothing about seasons. Curiously, the subcutaneous fat layer in humans is thicker than in other apes, perhaps in order to replace hair as insulation as the hair was lost for other reasons ....
(5) OR the selection pressure would work up to the point where it didn't matter much any more; the selection pressure would end when the appearance of bareness was just good enough. There is vast evidence of sexual selection of females for youthful appearance, and thus juvenile hair patterns would meet that selection criteria, without requiring that bareness be achieved.
(6) Selection pressure would work more on the sex that benefits from the apparent loss of hair: in humans the females are much more advanced in apparent bareness than the males, and the hair pattern in women is fairly consistent, while in men it varies considerably.
... the selection pressure would end when the ...
... selection goal is met, and the evidence is that it still continues:
(7) The evidence is that bare skin is still a factor in sexual selection, by the vast industry in hair removal equipment, salves, and treatements, some for men, but much more for women (also see Venus razor ads).
(8) Male hair pattern in women is seen as an unfortunate medical condition, female hair pattern in men is not.
(9) The porn industry is populated with fully shaved bodies, and a google for "hairy naked women" only shows women that have not shaved armpits and crotch, not women with beards.
Enjoy.
Mr Jack Message 49
(2) IF this were true THEN the most hairless appearing humans would be the hunters and not the gatherers. Conclusion: women did the hunting while the men did the gathering. Please compare this to what you know about anthropology.
African men are considerably more hairless than european men. It is quite plausible that the increased hairiness of men in Europe represents a trend of adaptation to colder conditions.
quote:
(3) This also explains why other cursorial hunters, like wild dogs and wolves, are naked ... ?
Those aren't persistance hunters. Humans are the only species in the world known to persistant hunt, AFAIK.
quote:
(7) The evidence is that bare skin is still a factor in sexual selection, by the vast industry in hair removal equipment, salves, and treatements, some for men, but much more for women (also see Venus razor ads).
(8) Male hair pattern in women is seen as an unfortunate medical condition, female hair pattern in men is not.
(9) The porn industry is populated with fully shaved bodies, and a google for "hairy naked women" only shows women that have not shaved armpits and crotch, not women with beards.
Using recent, predominantly western european fashions as evidence for long term evolutionary trends strikes me as absurd in the extreme.
quote:
RAZD Message 51
Hi Mr Jack,
To add to what Bluejay said,
African men are considerably more hairless than european men. It is quite plausible that the increased hairiness of men in Europe represents a trend of adaptation to colder conditions.
The telling issue is now how much different populations of men have different grades of apparent bareness, but the sexual dichotomy.
If an increase in apparent hairiness in men occurred as an adaptation to colder conditions, then why does it not also appear in women?
Any explanation for the apparent bareness of humans is incomplete at best if it does not explain the sexual dichotomy.
Sexual selection is the only mechanism I am aware of that explains the sexual dichotomy.
We know that many features of humans compared to chimps are due to neoteny. It is not logical that the selection for neoteny only selected facial features, rather than overall juvenile appearance, including the retention of juvenile hair patterns.
Again, there is no loss in the number of hair follicles, what we have is development of hair, particularly in women, arrested in a juvenile - vellus hair - stage.
Using recent, predominantly western european fashions as evidence for long term evolutionary trends strikes me as absurd in the extreme.
Riiight, I wouldn't dream of claiming that the present is the key to the past, and that, just because something is existing today, that it could have been existing in the past. ...yes?
Bluejay Message 50
Since Ken Fabos wants to focus on sensory functions of hair, maybe we could continue this discussion on why is the lack of "fur" positive Progression for humans?: I think there's still potentially a lot to be said for thermoregulatory functions of hairlessness.
I agree, and would be happy to discuss this further on that thread with anyone.
Enjoy
Mr Jack Message 52
Riiight, I wouldn't dream of claiming that the present is the key to the past, and that, just because something is existing today, that it could have been existing in the past. ...yes?
Sure, but using something we know has changed within the last hundred years and isn't culturally uniform as the basis for an argument is profoundly flawed.
I am not aware that the sexual dimorphism in hair patterns has changed in the last ~4000 years of recorded history, nor that archeological studies of early Homo sapiens artifacts show any reference to different hair patterns.
Again, the real issue is not so much explaining an apparent bareness of human beings, but to explain the sexual dimorphism that is evident between males and females.
Another discriminate characteristic of humans compared to apes is the neoteny evident in humans, particularly in femalse.
Neoteny - Wikipedia
quote:
Neoteny in humans can be seen in different aspects. It can be compared with other great ape species, between the sexes and between individuals. Some examples include:
  • the flatness of the human face compared with other primates
  • late arrival of the teeth
Compared with other species
The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Louis Bolk made a long list of such traits,[3] and Stephen Jay Gould published a short list in Ontogeny and Phylogeny.[4]
Between sexes
While neoteny is not necessarily a physical state experienced by humans, paedomorphic characteristics in women are widely acknowledged as desirable by men. For instance, vellus hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair through sexual differentiation, women do not, leaving their vellus hair visible.
This would suggest that the selection for vellus hair in women is part of the neoteny selection for young appearing females.
Sexual selection - Wikipedia
quote:
Charles Darwin conjectured that the male beard, as well as the relative hairlessness of humans compared to nearly all other mammals, are results of sexual selection. He reasoned that since, compared to males, the bodies of females are more nearly hairless, hairlessness is one of the atypical cases due to its selection by males at a remote prehistoric time, when males had overwhelming selective power, and that it nonetheless affected males due to genetic correlation between the sexes.
Which explains why the hairiness in men is highly variable, while the apparent bareness of females is very consistent.
Enjoy.
Edited by RAZD, : spling

we are limited in our ability to understand
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Replies to this message:
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 195 of 202 (561742)
05-22-2010 11:01 PM
Reply to: Message 190 by Dr Jack
05-21-2010 4:26 AM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Hi Mr Jack, sorry to take so long getting back to you.
I agree that the dimorphism between the sexes is down to sexual selection. Or, at least, it is involved in sexual signalling. The large beard of males probably serves a similar function to a Lion's mane.
Or the different facial hair patterns seen in males of many species of primates.
I'm unconvinced by the argument that hairlessness* of humans represents sexual selection.
What I really don't buy is your argument-from-recent-porn.
* - Yes, technically we're not hairless. You know what I mean.
Curiously, being unconvinced does not imply that it is not true, just that you have trouble accepting it based on the information available.
And it isn't an "argument-from-recent-porn" that I am making. What I've said is that IF this pattern of sexual selection still exists, that we should see evidence of it.
Particularly, if it is due to runaway Fisherian sexual selection, we should see evidence that goes beyond what is possible.
These studies have been done on facial characteristics for female beauty, with the result that an unreachable childlike appearance is found more desirable than what is genetically possible at this time.
Apparent bareness also fits this model, not just in modern porn but also in a whole industry devoted to hair removal:
Hair - Wikipedia
quote:
Though growing hair is an inevitable part of being human, many believe that it is unsightly and should be removed. Hair removal is almost always done for cosmetic reasons.
Again I refer you to the "Venus" razor ads.
And to documentation that "male hair pattern" in women is considered an undesirable medical condition.
It's multiple lines of evidence pointing in the same direction.
Message 94 Humans, male and female, are not neotenous. We have numerous paedomorphic traits (acquired at different points in our evolution) but the relative paedomorphy of traits reflects differing selective pressures through human evolution not a neotony event.
Neoteny\paedomorphy\tomatoe quibble. Meaning is the same in the end.
So you are claiming a number of discrete events while I am considering an overall long term trend that takes advantage of various mutations along the way, due to Fisherian runaway sexual selection that brings us to modern humans from ancestral apes.
If what is being selected are juvenile features in women capable of reproduction, then we should see a number of juvenile features in a state of arrested development when compared to other apes, and when compared to males.
Vellus hair is a juvenile feature.
This is the current average sexual dimorphism in humans, where the shaded areas are where androgenic (or terminal) hair grows. The bare portions are where vellus (or juvenile) hair grows.
Then there is the issue of blond hair ...
... and this
Enjoy.
Edited by RAZD, : added last image

we are limited in our ability to understand
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Rebel American Zen Deist
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This message is a reply to:
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Replies to this message:
 Message 197 by Dr Jack, posted 05-23-2010 4:34 AM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 196 of 202 (561743)
05-22-2010 11:12 PM
Reply to: Message 194 by Dr Adequate
05-21-2010 8:24 AM


Re: Neotony vs. paedomorphism
Hi Dr Adequate,
Not neceassarily. Consider the possibilities that (a) it was a side-effect of an adaptation for a non-neutral trait, which is what I suggested; or (b) it got fixed at some time before the human population was small and undispersed.
We also need to consider that what we are talking about is a juvenile hair pattern, rather than bareness.
It is unlikely that the juveniles were unfit.
Vellus hair - Wikipedia
quote:
The growth of vellus hair is of a different growth cycle than terminal hair.[3] When a person reaches puberty, androgen can cause much of the vellus hair to turn into terminal hair as well as produce new hair growth. In males this causes the changes in the vellus hair on the face and body. In both sexes it can produce the appearance of armpit and pubic hair.
While babies could be protected from cold by mom cuddling, this would be unlikely in prepubescent juveniles.
Enjoy.

we are limited in our ability to understand
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This message is a reply to:
 Message 194 by Dr Adequate, posted 05-21-2010 8:24 AM Dr Adequate has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 201 of 202 (564886)
06-13-2010 3:39 PM
Reply to: Message 197 by Dr Jack
05-23-2010 4:34 AM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
Hi Mr. Jack,
No, it isn't. The two are distinctly different in the genetics behind them, the protein changes that produce them and the overall effect on the organism one should expect.
And yet the end result is the same: juvenile features arrested in development and preserved in the adult form.
Neotony means that childlike features in one area are very likely to correlate with childlike features in another because they both have the same cause; paedomorphy doesn't share this feature.
So this would mean that the correlation of juvenile hair with other childlike features would mean that neotony is the correct term, rather than paedomorphy, yes?
Which does not surprise me given the source of the neotony comment ... this claim has been around for a while.
And it is common for further development of an organism to halt once sexual maturity has developed.
Interestingly I get a number of responses to googling "fficial&client=firefox-a]-->neoteny in humans-->fficial&client=firefox-a">neoteny in humans
Neoteny - Wikipedia
quote:
In developmental biology, paedomorphosis (also spelled pedomorphosis) or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Peramorphosis is change in the reverse direction. Paedomorphosis was first proposed by Walter Garstang in 1922[1]. The underlying mechanisms for this include heterochrony.
There are several kinds of paedomorphism which may appear independently or in combination:
• Neoteny, in which somatic (or physical) development is slowed, resulting in a sexually mature juvenile or larval form. ...
Ooo, it looks like it could be both ...
And, as the process that results in the paedomorphy is neotony, then it is more accurate to refer to it as neotony.
End result: sexual selection for juvenile appearance in sexually mature females has resulted in juvenile hair being arrested in development into mature hair in women.
It doesn't matter what you call it, the result is still the same.
Enjoy.
Edited by RAZD, : no smilies
Edited by RAZD, : mre accurate
Edited by RAZD, : again with the no smilies -- I don't know why this is not the default! (or at least stay checked once checked)

we are limited in our ability to understand
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Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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