Why do men have nipples, and why do both sexes have a dark area surrounding the teat? there is a theory that suggests that the nipples give the body a Larger face appearance, similar to the visual trick used by moths and butterflies.
Also of interest, there is a species of monkey that has a red nose area, blue cheeks and a yellow "beard", and by "chance" has a red penis, blue scrotum and yellow pubic hair. Which somehow supports the theory that the male nose & cleft chin gives an impression of a penis and a scrotum and the lips in a female's face gives an impression of a vagina.