Sigmund Freud proposed that the incest taboo is a reaction against unconscious, unacceptable desires.57 He suggested that the son is attracted to his mother (as the daughter is to her father) and as a result feels jealousy and hostility toward his father. But the son knows that these feelings cannot continue, for they might lead the father to retaliate against him; therefore, they must be renounced or repressed. Usually the unacceptable feelings are repressed and retreat into the unconscious. But the desire to possess the mother continues to exist in the unconscious, and, according to Freud, horror at the thought of incest is a reaction to, or a defense against, the forbidden unconscious impulse.
Freud’s theory may account for the aversion felt toward incest, or at least the aversion toward parent-child incest, but it, too, does not explain why society needs an explicit taboo, particularly on brother-sister incest. Nor does it account for the findings that support Westermarck’s hypothesis that familiarity breeds sexual disinterest.