Freud seeks at times very far fetched explanations for very simple phenomena in order to show the sexual motive at the bottom of them. He states in his Introduction to Psychoanalysis that a girl may show great affection for a younger sister "as a substitute for the child she vainly wished from the father." The truth is that the older daughter, in her close imitation of her mother, also starts "mothering" a child.
"A boy," Freud states in the same book, "may take his sister as the object of his love to replace his faithless mother." He rather imitates his father and starts to protect and order about a little female of his age, which at times, when both have witnessed the parental embraces, may lead to actual incest.
The Incest Fear. Incest is at the present day the form of sexual relation which provokes the most powerful expression of disapproval on the part of civilised and uncivilised races alike. In fact the primitive races seem obsessed by a panicky fear of incest. In many tribes, brothers and sisters are not allowed to meet or speak to each other and, in certain cases, they must even avoid the sight of each other and eschew every mention of each other's names.
In the Fiji Islands, where the rules against incest are especially rigorous, there are, on the other hand, special holidays on which orgies are held in which incest becomes permissible.
In other words, the natives of those islands, while recognising the irresistible nature of the incest temptation and taking all sorts of measures in order to prevent the commission of that sin, supply at stated intervals an outlet for incestuous cravings.
Innumerable details of primitive legislation separate the son-in-law from the mother-in-law, the father-in-law from his son's bride.
The Basogas of the Upper Nile loathe incest to such a degree that they punish it even in animals whenever it can be observed among them.
Incest in Ancient Times. The horror of incest, however, is a relatively recent development in human psychology and ethics. The ancient dynasties of Egypt and Peru practiced incest. Incest was indulged in by all the archaic gods. The authors of the book of Genesis must have accepted the idea of incest as the sole means of explaining Adam's and Eve's descendants.
The horror of incest which we all feel or pretend to feel, is indeed an acquired feeling. Since every race has adopted stern legal measures to prevent incest, it can only be because a desire for incest is one of the cravings which mankind is constantly struggling against.