We all know that incest is natural, but what do you think caused people to suddenly start seeing it as taboo on a widespread scale?

I am going to assume that either there was no taboo on incest before the 19th century and that suddenly people were shown a whole new perspective on the matter, or that the evidences against it were already known,<br>but ignored until they were brought to light during that period. Apparently, the fact that incest is immoral was not a common belief in western society before the 19th century, when evidence of the immorality of incest was finally obtained through the scientific method. But when and where exactly did the process of getting to those conclusions begin?<br>It seems as if the whole seasoned belief that incest is always wrong was created during that period of time.