When in history did people start seeing a girl's breasts as being inherently sexual?
score:7
Accepted answer
We know this goes back before history actually for at least two reasons.
They are depicted in exaggerated form in some of the earliest representational artwork we've found, way back in the Paleolithic era.
Their size on human females is far larger than is either necessary for milk production, or found in our closest relatives (the other Great Apes). The presumption has been that they have been selected for in our species due entirely to male preference for them.