this has always been a strange observation that i have had…
there doesnt’ seem to be any logical practical reason for this, it’s completely unfunctional.
Here’s Cecil’s take, at least regarding the pubic hair part.
I think Cecil’s article pointed towards hair being used to create scent, IIRC, to attract a mate.
I’ve always held the theory that at least part of the reason might be for a sexual aid. When people have sex, the hair above the penis can ‘tickle’ up against the general direction of the clitoris, helping climax. (Climax of course forces the cervix forward in the female, helping to ‘sop up’ the sperm deposit, so it has a reproductive purpose, not plain gratification). -And the hair around the labia would also create friction as the genitals bump together.
Of course, this theory depends upon the missionary position, which I’m not so sure our ancestors used mainly. I would WAG they were probably into ‘doggie’.
No one knows for sure, of course, but the best theories I’ve seen have to do with odor colletction and attraction by the opposite sex. There seems to be some data to suggest that women prefer the smell of men whose immune system is the most different from their own, presumably so that their offspring will have a more varied, and hence more effective, immune system. Not sure if I explained that correctly, but that is what comes to mind.
While that’s a popular belief it has precious little basis in fact. All female mammals can acheieve orgasm, and yet almost none ever do. If the purpios of orgasm is to increase fertility why did all our ancestral species have the trait ithout gaining any benefit?
Then we have the problem that most women orgasm either during foreplay or during copulation, before the male has ejaculated. Simultaneous orgasm is the exception rather than the rule. Why would a system evolve to be triggered by events that almost by defintion occur before the system can work. No semen present, no dice. There are those who argue for a major role for masturbation but this has too many problems associated with it to be credible.
Then of course we have no evidence at al that women that orgasm post coitus have any higher fertility rate.
Given that the evidence for orgasm serving a reprodcutive purpose is so thin on the ground, postulating that pubic hair evoled to promote this response is even less plausible.
While that’s a popular belief. Unfortunatley it has precious little basis in fact. All female mammals can achieve orgasm, and yet almost none ever do. If the purpoes of orgasm is to increase fertility why did all our ancestral species have the trait without gaining any benefit?
Then we have the problem that most women orgasm either during foreplay or during copulation, before the male has ejaculated. Simultaneous orgasm is the exception rather than the rule. Why would a system evolve to be triggered by events that almost by defintion occur before the system can work. No semen present, no dice. There are those who argue for a major role for masturbation but this has too many problems associated with it to be credible.
Then of course we have no evidence at al that women that orgasm post coitus have any higher fertility rate.
Given that the evidence for orgasm serving a reprodcutive purpose is so thin on the ground, postulating that pubic hair evoled to promote this response is even less plausible.
While with questions like this there isn’t a single right answer, there’s every reason to believe that one key explanation for this is that it was sexually selected; i.e., significantly more humans found that pattern alluring in their mates than other patterns. Never underestimate the power of sexual selection!
There’s a new theory that human hairlessness was selected for because people prefered mates that weren’t inhabited by fleas, ticks, lice, & other critters.
Biology Letters Online has the press-release and abstract posted, with the article itself available to subscribers.
The abstract:
True, however it would also work if the woman orgasmed after the man.
Maybe we need to switch foreplay for postplay?! 
Perhaps I’ve missed it, but I’m not sure the OP has been answered yet. It seems to me the question is not so much “Why do humans have armpit and pubic hair” but “If armpit and pubic hair is beneficial in some way, why are so many other wise hairy animals bereft of hair in those regions?”
RR
The question as posed has been answered: the pubic hair exists in those areas where the human equivalent of ‘scent glands’ are located. The hair provides a surface for evaporating these scents.
Why other animals don’t have pubic hair is too broad to answer. Some animals don’t have hair at all. Almost none have armpits. The genitals of the males are always tucked away beneath the body. The genitals of the females are out in the breeze. Other species have various ways of distributing their scent. Other species have much better sense of smell. Different social structures can make personal scent distribution of more or less value. Different hunting and hiding practices can demand different solutions.
Too many differences to provide any simple answer.