Human evolution and fur

[The Grand Nudger]

Minor correction. A hairless body does not make us more susceptible to heat, it makes us more susceptible to exposure. Evaporation by sweat on a hairless surface is orders of magnitude more effective than the same on a hirsute surface. We need to shed heat to do alot of things (think running down an antelope over the course of a few miles), and we need to shed heat even when we aren't doing anything (a drawback of our big brains). Some (read: most furry) animals pant to accomplish this, we are extremely limited in the panting department. We do have other means. Vasodilation, which is increasing the diameter of blood vessels particularly at skin surface (a good reason not to have an insulator over our skin surface). Decrease in metabolic rate, and sweating (sweating being another one that has a greater effect on a hairless body, as mentioned above).

Speaking of sweating, there are three types of sweat glands. The eccrine, apocrine, and sebaceous glands. Two of those are found attached to hair follicles (having sparse hairs attached to sweat glands which are otherwise exposed is a great way to increase surface area and therefore heat exchange-as well as a good way to "get your message out"...if you're feeling what I'm sendin..lol). The third, the eccrine gland is never found attached to hair follicles, it is however, found all over the human body. We have many many more eccrine glands than other mammals. It's a matter of available surface area. One of the greatest differences between ourselves and chimpanzees btw, the gene that codes for proteins that control the properties of our skin. A hell of alot of evolutionary work went into our surface area. Due to the characteristics of our skin human hair keratins are not as beneficial as the keratins of other species, we do not seem to have been selected for them, and they seem to have fallen by the wayside. This has the effect of making our "fur" much thinner than other animals fur. Those places where we have kept our fur are easily explained by the same means as those places where we did not. We see the loss of fur in our ancestors directly coinciding with the explosion of the size of our brain, which simply cannot function without a massive and superior cooling system.

It may not seem like this is such a definite advantage, but lemme give you an example of just how well we can exchange heat. In a marathon on a hot day, human beings can out-compete a horse (Daniel E. Lieberman of Harvard University and Dennis M. Bramble of the University of Utah). Not only can we out-compete the fuckers, we can do calculus while we run. Take that, bastards. Daddy needs a new bottle of glue.

So let's recap. Sweating increases physical performance (increasing our ability to secure food and/or avoid becoming food), allows for an extremely large brain, facilitates and advertises sexual availability, and is directed in large part (in human beings) by glands which are not found attached to hair follicles due to genes which code for proteins that have the effect of making those hairs we do have even thinner. One can see why the hairless ape was favored over the hirsute ape. The aquatic explanation fails to satisfy, we aren't large enough to shed fur for an aquatic environment and the gains in speed would be marginal as we are completely ill-equipped for swimming. Most aquatic predators interpret our swimming motions as a death-spasm. Small aquatic mammals are exceedingly furry, prized for their fur even. Large aquatic mammals can maintain temp easily through mass, mid size (think dolphins) are extremely active with high metabolic rates, they produce alot of heat. Parasites don't actually care if you're just a little bit hairy or a lotta bit hairy (case in point, we still get them), etc etc etc. Sweat glands are a major contributor to all evolution in mammals (the namesake itself being an extreme example) and the trend seems to have continued with ourselves. Thing is, we often get so caught up in "cause" we neglect the possibility of "causes". Sweating seems to have been the largest (and earliest) contributor, but that doesn't mean that it is the sole contributor. Climate change, a later addition of clothing, sexual preferences, the stillness of the air from ground level to about 3 feet and then the gentle breeze that increases above that level (upright vs all fours with regards to evaporation of water aided by moving air and the corresponding decrease of sweat glands in the majority of creatures below that level and increase above that level). Drag in water and air (think bats and whales- bats being a favorite of mine, the hairless wings are great for reducing drag and for increasing the effect of vasodilation, key, considering the vast amounts of heat created by all the energy and work that goes in to their flying while the rest of their bodies are hairy most likely due to their tiny mass and need to regulate a warm core temp especially while flying...at night). The permeability and general weatherproofing of skin (our own is pretty epic in this regard even among mammals). There is a veritable well-spring of evolutionary avenues that lead to a decrease in fur in our species and others. There are very few that would lead to an increase. It's very fucking cold, hair-so-thick- you can't bite through it, some chicks like teh furries......etc.
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