However, less is known about the innervation of nipples in men, studies on how nipple stimulation contributes to their sexual arousal are lacking, the researchers wrote. After all, sperm is cheap. When a woman's nipples are stimulated during breastfeeding, the neurochemical oxytocin, otherwise known as the "love drug," floods her brain, helping to focus her attention and affection on her baby. Since we don't get pregnant, and bear children, it doesn't cost us much to spread it around. Men are the only male mammals fascinated by breasts in a sexual context. But what purpose could this possibly serve? In the cultural view, men aren't so much biologically drawn to breasts as trained from an early age to find them erotic.
Why are heterosexual men so fascinated by women's breasts that we sometimes act as if the breasts are the seat of the soul?
Breasts: The Real Reason Men Love Them
So joke all you want, but our fascination with your breasts, far from being creepy, is an unconscious evolutionary drive prompting us to activate powerful bonding circuits that help create a loving, nurturing bond. The main job of breasts, of course, is to feed offspring. It's a behavior that males have evolved in order to stimulate the female's maternal bonding circuitry. If the main goal of sex -- evolutionarily speaking -- is to pass along one's genes, it would make more sense to have sex with as many women as possible, regardless of whether or not they looked like last month's Playmate. Notably, men often like nipple stimulation, too. Men are generally pretty happy to oblige.