In the social sciences and U.S. political discourse, the term "traditional family" refers to a nuclear family − a child-rearing environment composed of a breadwinning father, a homemaking mother, and their biological children; sociologists formerly referred to this model as the norm.[citation needed] A family deviating from this model is considered a nontraditional family. However, in most cultures at most times, the extended family model has been most common, not the nuclear family,[1] and the nuclear family became the most common form in the U.S. in the 1960s and 1970s.[2]