Jablonski: Yes it does. Those little chill bumps, or goose bumps, are caused by tiny little pieces of smooth muscle in the skin that cause the hairs on our body to stand up. When we had fur, this was really helpful because when the hairs stand up, it actually increases the insulating value of the hair. So if a dog is cold, or a squirrel, or a monkey or a chimpanzee is cold, his or her hair will stand on end and that will increase the outer insulation of the body.
Ours is pitiful. I mean we can see our hairs standing on end, but mostly we just see the skin getting sort of crinkled because of the contraction of these muscles. The hairs over most of the human body are so fine that they don't have any effect on insulation whatsoever. But it turns out that we haven't gotten rid of all of our hair because those little hair follicles turn out to be absolutely critical for healing of wounds. Every time we get a cut or a burn or anything that causes an abrasion or a change in the surface of the skin - an injury to the skin - the stem cells come from the hair follicles that enter into the repair of the wound. So those hair follicles turn out to be like little banks of future skin cells that are absolutely essential to the wound repair process.
CNN: Why do we still have armpit hair, pubic hair and hair on our heads?
Jablonski: The hair on the top of our heads is still a great protection from direct UV radiation. When you're standing at the equator, or near the equator, you're getting the highest levels of sun and UV radiation right on the top of your head. And so hair absorbs a lot of heat from the sun, and protects the scalp. Really curly hair is very good at this; really dark hair is good at this.
If you have dark hair yourself, you can verify this by sticking your fingers under your hair when it's sunny outside. The surface of your hair gets very hot, but the surface of your scalp is actually quite a bit cooler.
As for armpits and pubic hair, those hairs probably were retained for the propagation of pheromones, the scents that are so important in communication, although we do our best to get rid of these scents by showering every day and using all these products to get rid of smell. But these scents are really important in subconscious communication between humans. So these small areas of hair have been retained, but most of the body is naked so as to facilitate the loss of body heat through very rapid evaporation.
