stylistic:style_transfer, stylistic:tone, information:extraction
An incest taboo is any cultural rule or norm that prohibits sexual relations between certain members of the same family, mainly between individuals related by blood. All known human cultures have norms that exclude certain close relatives from those considered suitable or permissible sexual or marriage partners, making such relationships taboo. However, different norms exist among cultures as to which blood relations are permissible as sexual partners and which are not. Sexual relations between related persons which are subject to the taboo are called incestuous relationships. Some cultures proscribe sexual relations between clan-members, even when no traceable biological relationship exists, while members of other clans are permissible irrespective of the existence of a biological relationship. In many cultures, certain types of cousin relations are preferred as sexual and marital partners, whereas in others these are taboo. Some cultures permit sexual and marital relations between aunts/uncles and nephews/nieces. In some instances, brother–sister marriages have been practised by the elites with some regularity. Parent–child and sibling–sibling unions are almost universally taboo.