By looking at a person’s hair you can make assumptions about their age, ethnicity, gender, occupation, political views, their taste in music, income, lifestyle, religion, health, and sexuality. All from something that makes you want to puke if you find it in your meal.
Hair matters. For example, Vladimir Putin’s baldness may have helped him become president of Russia, as there is a joke among voters that Russian presidents should be alternately bald and hairy (and all male). Because Putin’s predecessor, Dmitry Medvedev, had a full head of hair, the thin-topped Putin was well suited to the role of president. The tradition can be traced back to 1925, alternating bald and hairy men have been in power since then.
One theory about why we have hair says that as our brains got bigger, we needed a way to get rid of all our excess brain-heat (brains are hot). By standing upright we decreased the amount of surface-area we had in the sun, while simultaneously evolving full-body sweat glands to encourage cooling evaporation. This evaporation is more effective with less fur. The hair on our heads is signal of youth and health, as hair tends to get less glossy, go grey, and thin out as we age.
Believe it or not, we still have as many hairs as our ancestors; they are just very hard to see. “Vellus” hair is very fine and usually almost invisible. It covers almost the entire surface of our skin, with the exception of our lips, the backs of the ears, the palms of hands, the soles of the feet, certain external genital areas, the navel, and scar tissue. These hairs only grow for a few months, as opposed to our head hair which grows for many years, and so never get very long. Our body hair still serves some function. It acts as a sensor, helps regulate body heat, and shields our eyes, nose, and ears from dust and debris.
So what about the highly visible and very ridiculous tufts of hair left on our naked bodies? Pubic hair, facial hair, and armpit hair is more mysterious than head hair. It is not clear why we have them. They seem to have developed separately to head hair. There are two species of louse that live entirely separately in head hair and pubes.
Pubic hair may serve to decrease chaffing friction during sex and to spread our sexy sweaty smells around better than skin, which is probably the reason we also have hair in our armpits. It also signals sexual maturity in a potential mate. Pubic hair is still puzzling though – most mammals tend to be less hairy around their genital area, not more hairy.