well, incest creates nothing but evolutionary dead ends, so it's unproven but not improbable that it being taboo across societies is at least influenced by genetics. The Egyptians didn't practice it as a society (if they had they certainly wouldn't have perservered for so long), their royals did, and records that prove they did it tell us nothing about how they felt about it. In fact European monarchies did it as a matter of course too, all the rulers of warring parties in the first world war could call each aother 'cousin willie' etc. Greek pederasty, a period of young adulthood where men are encouraged to have a love affair with a male adolescent for a couple of years, has, by definition, nothing to say from an evolutionary perspective, so is something of a non sequitur. The incest - placentophaghy comparison is that the lack of prevalence may* be genetically inspired, as may* be most peoples squeamishness towards the subjects. Which might also explain why some people may not have a problem/specific receptor. Aaaaaanyway, as you were. As said before, if that's what someone wants to do then more power them, let's hope its not actually harmful. *of course without some serious research/testing it's simply an unproven hypothesis, an opinion if you will.