Quote Originally Posted by Cilia View Post
Not all, but developed breasts are an indicator of female fertility, biologically speaking. (They develop during puberty, after all.) Thus, a female with visibly developed breasts is at least capable of producing offspring, even if they can't do so at this exact moment, and males will pay attention to her as a potential candidate for mating. (Yes, I am being cold and scientific about this. When such a question is asked, it requires that kind of attitude to be taken seriously.)
While it is true that many animals develop unique shapes specifically for the purpose of attracting mates (though, oddly, in most cases it's the male that has them, not the female), there's another theory I read about regarding the origins of the human shape that I found interesting, as well. The theory was that early humans developed the ability to evade predators by moving into deep water where the predators were reluctant to follow. With the enlarged, fatty breasts high on the chest, nursing mothers could continue to nurse even while hiding in this way. The theory was also an explanation as to why humans have so little body hair; like many mammals that spend a great deal of time in the water, extra body hair was superfluous.

Of course, none of this necessarily applies to Eorzean races. Evolution may or may not even be a thing in FFXIV, and the shapes of the various races may well boil down to "Haeydalyn created them that way".