Before central heating, pubic hair kept the genitals warm. The obvious advantage of warm genitals is that people would be more likely to take their clothes off, and men would be more likely to maintain an erection. Evolutionarily, the other function of hair was to draw attention to the genitals. (Evidently, it is not just modern men who seem to need a map to ensure they are heading in the right direction.) Pubic hair also decreases friction during intercourse, and I’ve seen some pretty nasty “rug burn” from rubbing while bare.
