A monogamous family is based on a legal or social monogamy. Several rodent species have flexible mating systems that can vary between monogamy, polygyny and promiscuity. They were largely but not completely successful in encouraging Shuar to abandon polygyny for monogamy. CE, both monogamy and polygyny occurred. Polygyny occurred even in areas of where monogamy was prevalent. The mating system of pinnipeds varies from polygamy to serial monogamy. It suggests an extreme inclination toward monogamy or committed relationships. Sexual monogamy is also rare among animals. Social monogamy, sexual monogamy, and genetic monogamy can occur in different combinations. Governments that support monogamy may allow easy divorce. Correspondingly, monogamy and commitment are more commonplace. The incidence of genetic monogamy may be estimated from rates of extrapair paternity. Other factors may also contribute to the evolution of social monogamy. As such, they are similar to the household formations created through divorce and serial monogamy. This pattern of serial monogamy is common among people in Western cultures.