Originally posted by Esau CairnMy anthropology professor once offered an interesting theory: basically it has to do with pair bonding.
But breasts are simply mammary glands to feed offspring...why is there a sexual aspect towards them?
The human infant requires very long-term care. This care is better assured with two parents. The way to better assure the two parents stay together, to establish more of an emotional bond, is for them to mate face to face, making eye-contact, as opposed to typical animal "doggie" style, where the male approaches the female's butt. How do you encourage face2face mating? Enlarge the female breasts so that cleavage resembles the female butt (eventually, millennia later, have the female wear red lipstick, and you further enhance "the front" mimicking "the back"😉.
No doubt this all evolved on a very subtle, unconscious level. But considering how "sophisticated" modern humans are, even today's female porn stars know why cleavage attracts (as Gianna Michaels once put it, it's like having an ass on your chest). 😎