Originally posted by Chi_archie
Evolution
Determining the evolutionary function of androgenic hair must take into account both human evolution and the thermal properties of hair itself.
The thermodynamic properties of hair are based on the properties of the keratin strands and amino acids that combine into a 'coiled' structure. This structure lends to many of the properties of hair, such as its ability to stretch and return to its original length. It should be noted that this coiled structure does not predispose curly or frizzy hair, both of which are defined by oval or triangular hair follicle cross-sections.[3]
Hair is a very good thermal conductor and aids both heat transfer into and out of the body. This is often seen as a problem with straighteners and blow drying as the hair quickly transfers the heat into the inner hair shaft and heats the water in the hair to boiling point resulting in dry brittle hair if silicone insulating oils are not used. When goose pimples are observed, small muscles contract to raise the hairs both to provide insulation, by reducing cooling by air convection of the skin, as well as in response to central nervous stimulus, similar to the feeling of 'hairs standing up on the back of your neck'. This phenomenon also occurs when static charge is built up and stored in the hair. Keratin however can easily be damaged by excessive heat and dryness, suggesting that extreme sun exposure, perhaps due to a lack of clothing, would result in perpetual hair destruction, eventually resulting in the genes being bred out in favor of high skin pigmentation. It is also true that parasites can live on and in hair thus peoples who preserved their body hair would have required greater general hygiene in order to prevent diseases caused by such as well as a need for grooming, two predominant factors in the civilization of homo sapiens.[4]
It had been believed that body hair was lost and replaced by increased fat storage. However, this is often found to be quite untrue, where people with excessive weight tend to also have increased body hair production. It is more correct to understand fat storage as a means of storing energy evolved due to infrequent sources of food being available commonly seen in people of African and Indian descent as well as some European peoples and hair production as a result of increased weight may be due to sensitive skin attempting to prevent abrasion where skin to skin contact may occur, e.g. under the chin.[5]
Notes
3 "Hair Shape". Hair-science.com. 2005-02-01. Retrieved 2009-09-18.
4 "Properties Of Hair". Hair-science.com. 2005-02-01. Retrieved 2009-09-18.
5 "Hirsutism (Excess Hair)". familydoctor.org. 1995-11-01. Retrieved 2009-09-18.
