In our modern culture we always seem to take for granted the fact that girls are expected to cover their breasts, with the (sometimes...) only real exception being breast-feeding, in which case the girl is still expected to cover her nipple.
This doesn't really make sense to me, as the only reason we see them as sexual is due to the fact we make them so illusive, similar to how Saudis are probably turned on by a girls hair, yet they're both not inherently sexual.
Breasts, unlike the anus, vagina and penis, do not expel waste, and aren't tools in intercourse, they're merely tools used to feed infants, yet they are still seen as equally taboo.
When did breasts become such a taboo, and why? What was so wrong with them that they needed to be covered? And why did it seemingly happen in multiple cultures that rarely, if ever, interacted or shared ideas?