On a number of occasions, Freud goes back to the hunter-gatherer days to illustrate how civilization has had major developments overtime. According to Freud, one of the first development had be was when the proverbial sons killed their father in the Bible. Having learned the value of cooperation, this according to him was an element of civilization. However, despite the vale that had been learned by the son, he was at the same time becoming burdened with guilt and remorse.
Although this is a historical fact, Freud doesn’t really substantiate these claims with any evidence. We are only left to assume that that’s how history went. This is an especially important point. Freud extrapolates a lot of his fundamental theories from examples in pre-history. If there were no truth to them at all, this might actually invalidate his theories.