Ah, on a further reading I think I see what you mean Woofie. But I believe you may have things vice versa. IMO it's less that human preference evolved to find large breasts attractive (in fact some cultures don't care for them) it's that in some places men just felt that way anyway, perhaps because it distinguishes male from female more, so chose partners that had the larger size boobs.
It's the same reason, for example, that peacocks have ridiculous tails to carry around: the peahens, over the generations, liked them. So the feature developed through partner preference, rather than preference developed for what was already in existence.
And it's most likely the same reason male youths are competitive, strong, aggressive etc. because young female youths like their partner that way, and choose them for procreation (and why middle aged men have beer bellies I'll bet).