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Author Topic:   why is the lack of "fur" positive Progression for humans?
RAZD
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Joined: 03-14-2004
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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 its 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/news/2002/12/1212_021213_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.ancestry.com/~gkbopp/DNA/HaploChart.htm


Click to enlarge

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.
http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1249263&pageindex=2
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.

http://mathildasanthropologyblog.wordpress.com/2008/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 couldnt 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


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cervical
Junior Member (Idle past 2726 days)
Posts: 2
From: United States
Joined: 04-23-2009


Message 182 of 202 (511906)
06-12-2009 3:58 PM


Im new here, and i havn't read this entire thread. I hope i'm not barging in...

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?

Im no expert in evolution, but traits that offer no advantage get lost in the gene pool.


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RAZD
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Posts: 19295
From: the other end of the sidewalk
Joined: 03-14-2004
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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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arrogantape
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Posts: 87
Joined: 09-26-2008


Message 184 of 202 (533530)
10-31-2009 4:26 PM


The new Scientific American issue has a story of h Floresiensis. The idea it is closely related to Homo Habilis has taken root. The similarities are significant. Size, brain capacity, tool making, and morphology link the two.

It seems non plausible to me that scientists staring at the Hobbit's feet don't entertain at least a fleeting thought the feet are great for water propulsion. Michael phelps had large feet, short legs, and a long powerful torso. The Hobbit is built the same, but with a downward curve of the clavicle, giving the hobbit a streamlined neck to shoulder shape.

Interestingly, the artist who created the model for the Hobbit pictured in Scientific American made her buck naked.

There needs to be an intensive search of shoreline caves in Africa, the middle east, all the way to Indonesia. I think it very unlikely H habilis, or H floresiensis will be found inland. They would stick to the coast, where the geology is fast changing. It's a tall order. I think islands will afford the best places to look.


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Hyroglyphx
Member (Idle past 102 days)
Posts: 5512
From: Austin, TX
Joined: 05-03-2006


Message 185 of 202 (533712)
11-02-2009 1:21 PM
Reply to: Message 184 by arrogantape
10-31-2009 4:26 PM


It seems non plausible to me that scientists staring at the Hobbit's feet don't entertain at least a fleeting thought the feet are great for water propulsion. Michael phelps had large feet, short legs, and a long powerful torso. The Hobbit is built the same, but with a downward curve of the clavicle, giving the hobbit a streamlined neck to shoulder shape.

Exercise cannot be genetically imparted to the progeny, so it is irrelevant. That large feet incidentally may have helped its survivability is something to look at, but it obviously didn't help the little Ebu Gogo enough.


"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence." --John Adams
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arrogantape
Member (Idle past 2252 days)
Posts: 87
Joined: 09-26-2008


Message 186 of 202 (533755)
11-02-2009 5:01 PM


Thanks for the reply. My point being that the unusual morphology of Phelps is behind his success. Long arms, long torso, short legs, long feet are great gear for swimming. The little hobbit lasted for a 100 thousand years in just that one cave. H habilis was a long survivor. The Hobbit is almost certainly derived from H Habilis, or the other way around. Whatever the genealogy hierarchy, The little guy did not swim to Flores from Africa. It was a slow procession along the shores by thousands of ancestors, beach by beach. My bet is they will never find this hominid again. Flores was unnatural as it had no large predators. That allowed the diminutive clumsy Hobbit to venture inland and establish a home there. Only on like no predator islands where you might find a cave with remains. Lets hope they do.
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RAZD
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Posts: 19295
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


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.

http://en.wikipedia.org/wiki/Flores

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.

http://en.wikipedia.org/wiki/Komodo_dragon

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
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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adelpit346
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Posts: 11
Joined: 04-05-2010


Message 188 of 202 (554755)
04-09-2010 10:21 PM
Reply to: Message 1 by LouieP
01-15-2008 12:27 PM


Spam

Edited by AdminSlev, : No reason given.


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RAZD
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Posts: 19295
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


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.

http://en.wikipedia.org/wiki/Neoteny#In_humans

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.

http://en.wikipedia.org/wiki/Sexual_selection#In_humans

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
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
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Replies to this message:
 Message 190 by Dr Jack, posted 05-21-2010 4:26 AM RAZD has responded
 Message 191 by Dr Jack, posted 05-21-2010 4:28 AM RAZD has acknowledged this reply

  
Dr Jack
Member
Posts: 3506
From: Leicester, England
Joined: 07-14-2003


Message 190 of 202 (561525)
05-21-2010 4:26 AM
Reply to: Message 189 by RAZD
05-20-2010 8:51 PM


Re: Mr Jack (and anyone else): Sexual Selection for Apparent Bareness
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.

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.


This message is a reply to:
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Dr Jack
Member
Posts: 3506
From: Leicester, England
Joined: 07-14-2003


Message 191 of 202 (561526)
05-21-2010 4:28 AM
Reply to: Message 189 by RAZD
05-20-2010 8:51 PM


Neotony vs. paedomorphism
This would suggest that the selection for vellus hair in women is part of the neoteny selection for young appearing females.

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.


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 Message 192 by Dr Adequate, posted 05-21-2010 5:52 AM Dr Jack has responded

  
Dr Adequate
Member
Posts: 15984
Joined: 07-20-2006
Member Rating: 4.2


Message 192 of 202 (561528)
05-21-2010 5:52 AM
Reply to: Message 191 by Dr Jack
05-21-2010 4:28 AM


Re: Neotony vs. paedomorphism
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.

This is a fine distinction; and I'm not convinced by your selectionism. It is at least plausible that (hormonal?) changes favored because they produced one selectively advantageous pedomorphic trait could as a side-effect have induced another which was neutral or even somewhat disadvantageous.


This message is a reply to:
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 Message 193 by Dr Jack, posted 05-21-2010 6:03 AM Dr Adequate has responded

  
Dr Jack
Member
Posts: 3506
From: Leicester, England
Joined: 07-14-2003


Message 193 of 202 (561530)
05-21-2010 6:03 AM
Reply to: Message 192 by Dr Adequate
05-21-2010 5:52 AM


Re: Neotony vs. paedomorphism
This is a fine distinction; and I'm not convinced by your selectionism. It is at least plausible that (hormonal?) changes favored because they produced one selectively advantageous pedomorphic trait could as a side-effect have induced another which was neutral or even somewhat disadvantageous.

It is plausible for that to happen, yes, almost all genes have multiple effects. However, the differing timing of the various paedomorphic traits means that there has been no overall neotony of the human form but rather multiple incidences of paedomorphy.

Hairlessness could be non-adaptive, but I find it unlikely. If hairlessness was a neutral trait we'd expect it to be more randomly distributed through populations.


This message is a reply to:
 Message 192 by Dr Adequate, posted 05-21-2010 5:52 AM Dr Adequate has responded

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 Message 194 by Dr Adequate, posted 05-21-2010 8:24 AM Dr Jack has not yet responded

  
Dr Adequate
Member
Posts: 15984
Joined: 07-20-2006
Member Rating: 4.2


Message 194 of 202 (561546)
05-21-2010 8:24 AM
Reply to: Message 193 by Dr Jack
05-21-2010 6:03 AM


Re: Neotony vs. paedomorphism
Hairlessness could be non-adaptive, but I find it unlikely. If hairlessness was a neutral trait we'd expect it to be more randomly distributed through populations.

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.


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 Message 193 by Dr Jack, posted 05-21-2010 6:03 AM Dr Jack has not yet responded

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 Message 196 by RAZD, posted 05-22-2010 11:12 PM Dr Adequate has not yet responded

  
RAZD
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Posts: 19295
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


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:

http://en.wikipedia.org/wiki/Hair#Removal_practices

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


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This message is a reply to:
 Message 190 by Dr Jack, posted 05-21-2010 4:26 AM Dr Jack has responded

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 Message 197 by Dr Jack, posted 05-23-2010 4:34 AM RAZD has responded

  
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