woah woah all these posts I didn't expect.
I step away for a minute to get food and this happens. Sorry sorry
Taz is on the right track with the answer though. Men were from the beginning of time genetically programmed to be attracted to traits in women that showed they were most capable of bearing children and feeding said children. This meant adult women that had developed bodies. Wide hips and full breasts were key signs for a ideal mating partner.
Being attracted to that kind of body is the most natural thing for a man to be attracted to.
People being attracted to other things, like prepubescent girls, or just underdeveloped girls in general. Emerged much later as people just arbitrarily decided they were going to be attracted to it.