Until the 1960s, it was widely assumed that marriage was a universal or nearly universal institution for licensing parenthood. Marriage assigned paternity rights to fathers (and their families) and guaranteed social recognition and economic support to mothers and their offspring. According to Malinowski (1930), who first articulated "the principle of legitimacy," and to Davis (1939, 1949), who extended Malinowski's theory into sociology, marriage provides the added benefit to children of connecting them to a wider network of adults who have a stake in their long-term development.

This functional explanation for the universality of marriage as a mechanism for legitimating parenthood became a source of intense debate in anthropology and sociology in the 1960s. Evidence accumulated from cross-cultural investigations showed considerable variation in marriage forms and differing levels of commitment to the norm of legitimacy (Bell and Vogel 1968; Blake 1961; Coser 1964; Goode 1961). More recently, historical evidence indicates that the institution of marriage was...