that in the 1200's, Thomas Aquinas, the pre-eminent Western (catholic) philosopher of around 500-1450, explained why incest is unacceptable.
He suggested that if you combine the love a man feels for a wife with the love a brother feels for his sister it would create in such a tremendous amount of affection as to result in unduly frequent intercourse, this constant sex-having would not leave enough time to worship God.
What is more shocking about this? The gross stupidity, or the fact that it took Catholics 1200 years to come up with a reason not to fuck your family and this is the best they could do...
This is really interesting to me not just because its funny, but because it is an instance where proper morality ABSOLUTELY CANNOT be traced to religion, it comes form science. The only real reason not to engage sexually with familial relations is because of evolution, it increases the risk of all manner of diseases, which may be why Prince Charles looks like that.
All praise science.