Various cultures have had their own theories on the origin of marriage. One example may lie in a man's need for assurance as to paternity of his children. He might therefore be willing to pay a bride price or provide for a woman in exchange for exclusive sexual access. Legitimacy is the consequence of this transaction rather than its motivation. In Comanche society, married women work harder, lose sexual freedom, and do not seem to obtain any benefit from marriage. But nubile women are a source of jealousy and strife in the tribe, so they are given little choice other than to get married. "In almost all societies, access to women is institutionalized in some way so as to moderate the intensity of this competition." Forms of group marriage which involve more than one member of each sex, and therefore are not either polygny or polyndry, have existed in history. However, these forms of marriage are extremely rare. Of the 250 societies reported by the American anthropologist George P. Murdock in 1949, only the Caingang of Brazil had any group marriages at all.
Various marriage practices have existed throughout the world. In some societies an individual is limited to being in one such couple at a time , while other cultures allow a male to have more than one wife polygyny or, less commonly, a female to have more than one husband (polyandry). Some societies also allow marriage between two males or two females. Societies frequently have other restrictions on marriage based on the ages of the participants, pre-existing kinship, and membership in religious or other social groups.