What's the point of pubic hair?

Dear Big Scary Man with a Piece of Cheese,  

You and your friends have stumbled upon one of the eternal mysteries of the human body. There are a number of theories on why pubic hair exists, but no definitive answer. However, most sources agree that pubic hair relates to pheromones—scents that the body produces that can be sexually stimulating to others.

Believe it or not, humans have the same number of hair follicles as apes, except our body hair is generally very fine or barely visible in comparison. Pubic and underarm hair, on the other hand, tends to be more visible and coarse. This difference is due to the fact that humans have two types of hair on our bodies: vellus hairs (which are shorter and thinner) and terminal hairs (which are longer and thicker). Pubic hair consists of terminal hairs. Both types of hair consist of visible shafts and deeply-embedded roots surrounded by follicles. At the base of hairs is a bulb which allows new cells to form and for new hair to grow. It's believed that the tufts of hair around the genitals, as well as under the arms, release pheromones, which may act as erotic stimulants for sexual partners.

Pheromones get trapped in pubic hair when apocrine glands release an odorless secretion on the surface of the skin that combines with bacteria decomposed by the secretions of the sebaceous glands. The resulting scent is different for individuals due to a genetic complex called the major histocompatibility complex (MHC). Studies suggest that people are attracted to those with very different MHCs than their own, perhaps because genetically diverse offspring may be more able to fight off disease. For some people, scents from these areas are noticeable and consciously increase sexual arousal. For others, pheromones might not be obvious but may be detected subconsciously.

There are other hypotheses about why we have hair on our pubic places. Some people believe that it keeps our genitals warm. In prehistoric times, when only a loincloth was worn to cover the penis or vulva, this might have held true. However, if the primary job of pubic hair was to keep the genitals warm, the shaft of the penis, the scrotum, or the lower torso of people with vaginas would likely have more hair to insulate the reproductive organs (e.g. testes, ovaries). 

An additional theory suggests that the purpose of pubic hair for people with vaginas is similar to that of cilia in the nose (a.k.a., nose hair) and eyelashes. In this case, the pubic hair prevents dirt and particles from entering the vagina. However, one problem with this theory is that people with penises don't have similar protective hair around the opening of the urethra.

Evolutionary scientists suggest that humans may have evolved to have less pubic hair to appeal to the opposite sex: a form of sexual selection. Hairlessness meant that there was a lower chance that a person would carry parasites. Indeed, most pubic grooming for those with penises was historically done to reduce parasitic risks. On the other hand, there are records from as early as the medieval era of people with vaginas grooming their pubic hair to increase sexual attractiveness—a practice that many still engage in today.

As far as non-functional use goes, pubic hair can be decorative or attractive to their owners or to others. It may be cut or styled in ways to appeal to sexual partners, which may increase sexual potential, at least in theory. Research has found that the grooming of pubic hair correlates with an increased number of sexual partners and that some people prepare to have sex by shaving or grooming their pubic hairs. Furthermore, pubic grooming is often considered a sign of attractiveness or cleanliness in popular culture. That being said, different cultures may have preferred norms for pubic hair, ranging from completely removed, to styled, to natural.

As with any unsolved mystery, there are probably other theories out there regarding the purpose of pubic hair, so don't be too hard on your friends if they can't answer your question.