I have wondered this very thing myself. So I set about finding an answer.
As with most "why" questions posed to scientists, the answer is, in two words, "Nobody knows." Many theories have been posited, and some are preferred over others, but no particular theory has the scientific community's wholehearted endorsement.
That said, I will relate these theories to you. But first, a few words on the nature of pubic hair.
As most of you are aware, pubic hair emerges on the body at adolescence, that lovely, happy time when your body is thoroughly changing itself and your peers are being absolutely merciless to you and everyone else.
This junior high theater troupe is smiling and giving the thumbs-up sign. Could they be saying, "Hooray! Puberty!"
(Photo from Actors Equity.org)
Pubic hair makes its appearance in response to that onrush of hormones that happens at adolescence. Boys and girls both get a flood of male hormones working in their system. It's the male hormones that stimulate hair growth -- as well as increased muscle strength and deepening the voice and so on -- and they make the hair in your pubic area and your armpits spring into action. These male hormones are known collectively as androgens. Therefore, the hair you get at your special parts is referred to as androgenic hair.
The fact that your pubic hair arrives on the scene at the time when your body gets ready to be sexually active and reproducing cannot be an accident. Therefore, the explanation for pubic hair probably relates to matters reproductive.
Current Favorite Theory - Pheromone Dispersal
The favorite theory about the reason we have pubic hair is at the top of the list because it connects most closely with matters of reproduction. This theory is that pubic hair helps pick up, hang onto, and disperse to the four winds our pheromones. Pheromones are chemicals that many animals produce to signal to other members of their species of their presence. Sex pheromones act particularly powerfully on same-species opposite-sex animals. They say, "I'm here, mate with me."
The idea is that the pubic hair gives a whole lot more surface area where the pheromones can collect, and thus we are better able to distribute our scent so that potential partners can get turned on and come find us to mate with us.
The problem with this theory is that scientists have had trouble demonstrating, without doubt and over and over again, that people respond to other people's sex pheromones. They have shown for sure that other animals do, but they've had trouble proving it when it comes to human interaction. Despite this difficulty, people seem reasonably sure that we do respond to each others' pheromones, however faintly we might perceive them.
A corollary to this theory is that whether or not pheromones are involved, there is a definite scent that the glands around our groins emit. Pubic hair helps to collect and perhaps intensify that scent, thus increasing the power of our "I'm ready to mate" signal.
Some other theories that have been tossed about but generally rejected for various reasons include:
- To keep the blood-rich and sensitive areas of our bodies extra warm. Objections to this theory include the fact that we now wear clothing, so wouldn't pubic hair therefore be obsolete?
- To trap dirt particles and other nasties and keep them from entering a woman's vagina. The major objection to this theory is, why isn't men's pubic hair similarly dispersed so that it could fulfill a similar function?
- To be another form of visual display in attracting a mate. This one is problematic because we don't go around showing our pubic hair to people, at least not right off the bat.
- To give babies another sort of handhold to grab onto. Again, the problem with this theory is that we usually don't go around picking up and taking care of babies while we're naked. Also, babies find a heckuva lot of things to grab onto; I don't think they really need your armpit hair to pull themselves up. And a baby grabbing onto your pubic hair? No thank you!
Could this baby really be thinking, "I want to stand up, where's your pubic hair?"
(Photo from Fisher-Titus Medical Center)
- To provide additional lubrication against chafing in these areas where joints are especially active. I like this theory in part because if you do a lot of walking, you're pretty grateful you've got that extra cushion. But the problem here is that I, for one, shave my armpits, and I'm more likely to get razor burn than I am to suffer chafing due to the absence of that extra cushion of hair. Also, this theory doesn't really have anything to do with matters reproductive.
- To lend additional sensitivity to these crucial parts of the body. This theory is my own. When you slowly bring your hand close to your forearm, say, the hairs on your arm tell you, before your hand touches your arm, that something is very close and is about to touch you. Wouldn't that be an extra benefit for your highly sensitized genitals? Wouldn't that be a useful feature in matters reproductive? The problem with this theory is that similar hair is also present at your armpits, and that area is not directly involved in the act of reproduction. So while I like parts of my own theory, I'm going to have to agree with everybody else I've read on this subject and say that I like the pheromone dispersal theory the best.
Personally, I think the pheromone/scent dispersal theory is probably the most likely. Well, I don't know about pheromones necessarily, but I'm going to bet that some sort of scent dispersal happens, or is further assisted by, the pubic & armpit hair. It's your body's way of saying, "Hey, I'm sexually mature, and I'm a little bit warmed up already, so come mate with me." Whether you approve that message or not, your body seems to go ahead and say it.
For more about hair elsewhere, check out a very brief entry on head hair and another entry on nasal hair.
A Health Blog, The Human Hair
Wikipedia, Androgenic Hair and Pubic Hair
Howard Hughes Medical Institute, Pheromones and Mammals
Deb Levine, "Pheromones: Potential participants in your sex life," CNN, June 25, 1999
Go Ask Alice! What's the point of pubic hair?
Ask the Sexpert, What is the purpose of pubic hair?
The Straight Dope, What's the purpose of pubic hair?
Katie Grace, Column: Does pubic hair serve a purpose? The News Record, April 7, 2004
Yahoo! Answers, What is the purpose of pubic hair?