Final answer:
The prohibition of sexual relations and marriage between close kin is known as the incest taboo. This taboo is present in all cultures and extends to relations considered too close for sexual relationships. It separates individuals into biological family ties and potential sexual partners.
Step-by-step explanation:
Across all cultures, there is an incest taboo, a cultural norm that prohibits sexual relations between parents and their offspring. This taboo sometimes extends to other relations considered too close for sexual relationship. In some societies, this taboo may extend to first cousins. French anthropologist Claude Lévi-Strauss argued that incest is the original social structure because it naturally separates groups of people into two types-those with whom an individual has family ties (so-called biological ties) and those with whom an individual can have sexual relations and establish ties.