Before you say, “Duh…”
…researchers at Emory University think human evolution and the neurochemical oxytocin a.k.a. “the love drug” are responsible for straight men’s near - universal obsession with breasts.
A neural circuit that evolved to strengthen the mother-infant bond during breastfeeding can help strengthen the bond between couples as well. When a woman's nipples are stimulated, oxytocin floods her brain, helping to focus her attention and bond with her baby, but new research has shown that this circuitry may not be reserved only for this purpose.
During foreplay and sex, when a partner kisses, touches and massages a woman's breasts, this triggers the release of oxytocin, but in this context, the oxytocin focuses the woman on her partner, strengthening her desire to bond. Men may be programmed to stimulate women's breasts because it makes them more desirable…to women. Breast play may be an adaptive strategy for bonding and mating.
"Evolution has selected for this brain organization in men that makes them attracted to the breasts in a sexual context, because the outcome is that it activates the female bonding circuit, making women feel more bonded with him. It's a behavior that males have evolved in order to stimulate the female's maternal bonding circuitry.”
Science has a knack for making fun things sound boring, but I doubt this new information will make men love breasts any less.
Source: LiveScience: http://www.livescience.com/23500-why-men-love-breasts.html?cmpid=514626_20150901_51744756&adbid=10153124752876288&adbpl=fb&adbpr=373856446287