What is the evolutionary advantage of having pubic hair?
Many consider pubic hair to be a sort of protection or warmth, however this can only hold true for the vagina, since pubic hair doesn't offer any additional protective advantages to the male urethra. The most prevailing theory is that simply it is one of the odor producing parts of the body and humans (like most life forms in general) are simply aroused by strong smells. Also most odour producing parts are usually accompanied by hair in order to "catch" pheromones. It is notable that those odours are not the direct product of glandular secretions, as those secrations are in fact odorless. It is their combination with bacteria that gives every person a unique smell. This unique smell gives a lot of important information to the canditate sexual partner. Here is an interesting study about odour importance in sexual reproduction as well as the role of MHC(Major Histocompatibility Complex)

If you are interested you can read further for for the Importance of smell in sexual production