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Author Topic:   why is the lack of "fur" positive Progression for humans?
molbiogirl
Member (Idle past 1917 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 6 of 202 (449645)
01-18-2008 3:31 PM
Reply to: Message 4 by dwise1
01-18-2008 2:43 PM


Ever try to run long distances in a fur coat?

Yup.

Dissipation of heat is the function that most conspicuously distinguishes human skin from that of all other animals. Removal of excess heat is greatly facilitated by the loss of body hair because it increases thermal conductance and permits additional heat loss through sweating.

A strong case can be made for the evolutionary loss of apocrine sweat glands in humans because these sweat glands are most common in heavily furred animals. The African apes exhibit a ratio of approximately 40% apocrine sweat glands to 60% eccrine; the great preponderance of eccrine sweat glands in modern humans probably evolved under the strong influence of natural selection, following the loss of the apocrine glands.

This process was probably propelled by increases in body size and activity levels associated with modern limb proportions and striding bipedalism.

And you very nearly nailed the title of a paper, dwise!

The Energetic Paradox of Human Running and Hominid Evolution
Current Anthropology, Vol. 25, No. 4 (Aug. - Oct., 1984), pp. 483-495

There is also this:

A naked ape would have fewer parasites
Proceedings of the Royal Society
Volume 270, Biology Letters Supplement 1 / August 07, 2003

According to this paper ...

Evolution of nakedness in Homo sapiens
Journal of Zoology 273 (1), 1–7.

... there are a dozen different hypotheses.

The cooling device hypothesis
The hunting hypothesis
The bipedality hypothesis
The allometry hypothesis
The clothing hypothesis
The vestiary hypothesis
Neoteny hypothesis
Carrion-eating hypothesis
Sex-related hypothesis
Aquatic ape hypothesis
Adaptation-against-ectoparasites hypothesis

The author kicks the snot out of all of them -- except parasites and ornamental.

As the ectoparasite burden on hominids increased, having fewer parasites may have become more important for survival than a warm fur coat. Natural selection may have started to favour shorter-haired and less parasite-ridden individuals, leading to the naked ape of today (Rantala, 1999). Selection pressure towards nudity may have been enforced by the many lethal diseases that are carried by blood-sucking ectoparasites. For example an outbreak of typhus, various forms of spotted fever, bubonic plague or any similar pandemic could have wiped out an entire fur-bearing segment of the human population (Olson, 1966).

This ‘naked skin’ makes humans more vulnerable to UV radiation and to both high and low temperatures (Amaral, 1996). Furthermore, fur would protect humans from wounds, sores and insect bites, which may cause serious inflammations. A hairy individual also looks larger, which confers an advantage especially in sexual selection and in defence against predators. Thus, nakedness causes many clear costs for the naked ape.

In The Descent of Man, and Selection in Relation to Sex, Darwin argued that man, or rather primarily woman, became divested of hair for ornamental purposes and that women subsequently transmitted the sexual advantage of nakedness almost equally to their offspring of both sexes. Darwin (1871) had also collected evidence that many species had evolved features that were in themselves inconvenient or injurious, but that were retained because they were attractive to the opposite sex.


This message is a reply to:
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molbiogirl
Member (Idle past 1917 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 17 of 202 (449721)
01-18-2008 8:35 PM
Reply to: Message 10 by RAZD
01-18-2008 7:40 PM


This is either another example of neoteny in humans or it is the raison d'etre for neoteny (ie sexual selection for younger appearing females).

According to this guy ...

Evolution of nakedness in Homo sapiens
Journal of Zoology 273 (1), 1–7.

... there are a couple of problems with neoteny.

It has been suggested that humans are a juvenilized form of ape (Gould, 1977). ... If the hairlessness of the foetal ape was being retained into adulthood by a process of neoteny, one would expect the human body to retain this characteristic throughout its whole development from embryo to adult. However, this is not the case. When the human foetus is 6 months old, it becomes completely covered with a coat of fine hair known as lanugo. Normally, this hair is shed long before birth; occasionally, a baby is born still wearing its woolly coat, only to lose it within the first days after birth (Morgan, 1982).

Another weakness of the theory is that while some characteristics may be retained as part of a neotenic package, this only applies to characteristics that are either benign or neutral in their effect on fitness to survive. No one claims that all foetal characteristics are retained in a neotenic species. For example, a human foetus and a human baby both have very short bandy legs, but natural selection ensures that this feature is not retained in adult life (Morgan, 1990). Furthermore, the neoteny theory does not tell us anything about the value of nudity as a new character that helped the naked ape to survive better in his hostile environment (Morris, 1967).

Ditto for sexual selection.

Furthermore, expensive sexual signal for the purposes of sexual selection are usually seasonal, and generally develop after sexual maturation. Although H. sapiens males are generally considered to prefer less hairy females (Darwin, 1871), and sexual selection may have facilitated the evolution of nakedness (Rantala, 1999; Pagel & Bodmer, 2003), Darwin's hypothesis does not explain what initial selective advantage would have caused males to start to prefer more naked females (see Fisher, 1930; Kokko et al., 2002).

Another author points out that it is unusual in sexual selection to have the same trait selected for in both sexes.

Evolution Theory and Practices
Eviatar Nevo, Solomon Pavlovich Vasser, 2004, p. 334

Although Dawkins seems to think that when one sex evolved "ahead" of the other, the other sex can be "dragged in its wake".

The Ancestor's Tale
Richard Dawkins, 2004, p. 264


This message is a reply to:
 Message 10 by RAZD, posted 01-18-2008 7:40 PM RAZD has replied

Replies to this message:
 Message 23 by RAZD, posted 01-18-2008 9:30 PM molbiogirl has replied

  
molbiogirl
Member (Idle past 1917 days)
Posts: 1909
From: MO
Joined: 06-06-2007


Message 30 of 202 (449778)
01-18-2008 11:04 PM
Reply to: Message 23 by RAZD
01-18-2008 9:30 PM


It isn't. It is selected in women, males just inherit it. Look at the variation in males versus women.

That still doesn't address the initial reason for sexual selection. Why allofasudden is nekkid pretty?


This message is a reply to:
 Message 23 by RAZD, posted 01-18-2008 9:30 PM RAZD has replied

Replies to this message:
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