Why is it that heterosexual men love breasts? It's probably a question that many men have never bothered to ask and simply stick with the answer: "Just like 'em, don't I." But evolution has certainly played a big part in this because, essentially, playing with a woman's breasts during foreplay helps her feel closer to her partner, which is something the other participant also enjoys.
In 2012, two male researchers finalised the research that they had compiled for some time to answer the question that seemingly needs no answer. Larry Young, director at the Center for Translational Social Neuroscience, and Brian Alexander wrote in a piece for the Huffington Post: "Some evolutionary biologists have suggested that full breasts store needed fat, which, in turn, signals to a man that a woman is in good health and therefore a top-notch prospect to bear and raise children."
Taking the more David Brent approach to it, they say: "Another hypothesis is based on the idea that most primates have sex with the male entering from behind. This may explain why some female monkeys display elaborate rear-end advertising. In humans, goes the argument, breasts became larger to mimic the contours of a woman's rear."
However, they then say that both of these theories are myths. We now know that when a woman breastfeeds her infant, her nipples becomes stimulated and neurochemical oxytocin rushes to her brain to help her maintain focus and effort into feeding her baby.
It's a similar chemical response during intimacy too. Nipple stimulation during foreplay activates the same part of the brain as clitoral stimulation. Oxytocin is released in the brain and the same focus and care is heaped upon the woman, giving her a sense that she wants to get closer to her partner as it makes him seem more desirable.