The incest taboo is a universal rule, that is, it is present in all human societies for which there is an ethnographic record. It consists in prohibiting the occurrence of sexual and marital relations between close relatives, as occurs between parents and children and siblings. Its existence would not have resulted from genetic problems, as many imagine, but, above all, from socio-cultural issues, such as the need for social relations guided by reciprocity and alliance between families. If it were a prohibitive rule determined biologically, there would certainly be a taboo of incest among non-human primates, felines, canids, cattle, etc. Therefore, kinship is a relationship constructed socially and culturally, as it happens, just to exemplify, between parents and adopted children.
The recognition and classification of relatives varies from one society to another and there are the most complex rules on incest. An example of this is society the father's brother is called the uncle, the paternal uncle. In certain indigenous societies he is also considered a father and, therefore, his children are brothers (not cousins) of his brother's children. In such cases, the recognition of who is a brother implies knowing with which relatives it is forbidden to have sexual and marital relations. There is, however, the registration of marriage between brothers in ancient Egyptian royalty and among the Incas, among others, but they are exceptions to the rule.
