When Did Our Ancestors Lose Their Hair?

[shawnhcorey]

Assuming as you say, that hairier individuals, having be burned by it, chose to avoid it altogether, the adaptive advantage on those who decided to stick with it would be substantial, And it would seem to me obvious that the less hairy would be prominent amongst the stickers.

 

That's what I said, the less hairy would stick with it. That means, of course, that they were less hairy to start with; something else cause they to evolve the reduction of hair.

[Mike Waller]

That's what I said, the less hairy would stick with it. That means, of course, that they were less hairy to start with; something else cause they to evolve the reduction of hair.

 

 

Natural variability is one of the bedrocks of evolution. A re-occuring mutation which might once have been an actual disadvantage or a disadvantage in terms of acceptability in the context of sexual selection, suddenly becomes something positive. There does not have to have been an environmental factor that favoured it previously. Which is not, of course, to say that there wasn't something that did so favoured it.

[Santalum]

Natural variability is one of the bedrocks of evolution. A re-occuring mutation which might once have been an actual disadvantage or a disadvantage in terms of acceptability in the context of sexual selection, suddenly becomes something positive. There does not have to have been an environmental factor that favoured it previously. Which is not, of course, to say that there wasn't something that did so favoured it.

 

Surely there can be no other logical explanation other than the fact that humans, unlike all other mammals, have very well developed sweat glands as a means of cooling ourselves and that sweating does not work with a full or signficant coat of hair.

 

Combined with the fact that humans are accomplished persistance hunters where long endurance under sustained exertion, that no other mammals possess, is absolutely essential.

 

It is pretty clear that there would be strong selection pressure for hairlessness under the above circumstances.

 

The other apes are not persistance hunters and hence there has not been as strong selection for hairlessness among them.

 

Apocrine sweat glands are larger, have different mechanism of secretion, and are limited to axilla (armpits) and perianal areas in humans. Although apocrine glands contribute little to cooling in humans, they are the only effective sweat glands in hoofed animals such as the donkey, cow, horse, and camel.^[2][3] Most other mammals, such as cats, dogs and pigs, rely on panting or other means for thermal regulation and have sweat glands only in foot pads and snout. The sweat produced on pads of paws and on palms and soles mostly serves to increase friction and enhance grip.

 

Presumeably this type of sweat gland in hoofed animals is not as effective as, from inumerably documentaries, human hunters are nearly always able to run down hoofed animals as long as they can track them. I believe that hoofed animals are still reliant on panting etc to some extent to assist in cooling themselves and they have to stop running in order to do that.

 

Abstract

Mammals have two kinds of sweat glands, apocrine and eccrine, which provide for thermal cooling. In this paper we describe the distribution and characteristics of these glands in selected mammals, especially primates, and reject the suggested development of the eccrine gland from the apocrine gland during the Tertiary geological period. The evidence strongly suggests that the two glands, depending on the presence or absence of fur, have equal and similar functions among mammals; apocrine glands are not primitive. However, there is a unique and remarkable thermal eccrine system in humans; we suggest that this system evolved in concert with bipedalism and a smooth hairless skin.

 

http://books.google....olution&f=false

 

Also from this website it is more specifically day time persistance hunting that produced strong selection pressure for hairlessness in humans. A great many other predators hunt mainly at night when it is cooler.

 

Persistence hunting is a hunting technique in which hunters use a combination of running and tracking to pursue prey to the point of exhaustion. While humans can sweat to reduce body heat their quadruped prey would need to slow from a gallop to pant.^[1] Today, it is very rare and seen only in a few groups such as Kalahari bushmen and the Tarahumara or Raramuri people of Northern Mexico. Persistence hunting requires endurance running – running many miles for extended periods of time. Among primates, endurance running is only seen in humans, and persistence hunting is thought to have been one of the earliest forms of human hunting, having evolved 2 million years ago.

 

 

Contents

[hide]

• 1 Persistence hunting in human evolution
• 2 Procedure
• 3 Persistence hunting among cultural groups
• 4 See also
• 5 References
  • 5.1 General
  • 5.2 Notes

  [*]6 External links

Persistence hunting in human evolution

Further information: Endurance running hypothesisThe persistence hunt may well have been the first form of hunting practiced by hominids. It is likely that this method of hunting evolved before humans invented projectile weapons, such as darts, spears, or slings. Since they could not kill their prey from a distance and were not fast enough to catch the animal, one reliable way to kill it would have been to run it down over a long distance.

 

In this regard one has to bear in mind that, as hominids adapted to bipedalism they would have lost some speed, becoming less able to catch prey with short, fast charges. They would, however, have gained endurance and become better adapted to persistence hunting.^[2] Although many mammals sweat, few have evolved to use sweating for effective thermoregulation, humans and horses being notable exceptions. This coupled with relative hairlessness would have given human hunters an additional advantage by keeping their bodies cool in the midday heat.

 

 

Edited February 1, 2012 by Santalum