system
A chat on subreddit /r/me_irl
human
Small tits lactate just as well though. If anything, large ones are more an indication that a woman recently gave birth. While this pretty much the ultimate sign of fertility, it also means that the woman already likely has a mate. Really I can't think of a satisfying evolutionary psychology reason for the preference. Though there are many things like that. For instance, why is facial symmetry attractive to many? So many things are so arbitrary.
gpt
&gt;While this pretty much the ultimate sign of fertility, it also means that the woman already likely has a mate. 

Monogamy is probably too new on human society to have any impact in evolution yet.