Although family is difficult to categorize because of its diversity, anthropologists have defined four basic family types that are duplicated across cultures with minor variations. Each of these types is adapted to the social and economic needs of the family unit and is normally associated with particular subsistence strategies. Some families change to address immediate needs, such as when elderly parents can no longer live on their own independently. Regardless of its type, the family unit is a remarkably adaptive cultural mechanism. Nuclear families: Also known as a single-couple family, a nuclear family is composed of one or two parents and their immediate offspring. It is the smallest family structure and is often found in societies where geographic mobility is valued. The nuclear family is common in small-scale foraging societies (bands) and industrial/postindustrial and market societies (states), both settings in which subsistence activities require families to relocate with some regularity. Although the model of the American nuclear family consisting of a two-parent household with one or more children has become less typical over the last several generations, it continues to be a norm. As of the 2016 census, 69 percent of US children under the age of 18 were living in a two-parent household, a decrease from 88 percent in 1960. There are, however, other kinds of nuclear families. In the 2016 US census, 23 percent of children under 18 were living in a female single-headed household (mother), almost triple the number living in female single households in 1960 (8 percent). There was also an increase in children under 18 living in male single households (father), from 1 percent in 1960 to 4 percent in 2016 (United States Census Bureau 2016; Kramer 2019). Another growing nuclear family type is same-sex families. These may or may not include children. In the 2020 census, 14.7 percent of the 1.1 million same-sex couples in the United States had at least one child under 18 in their household (United States Census Bureau 2020). In cases where the alliance between adults is temporary or informal, these families may be nonconjugal nuclear families or cohabitation families. (Note: The above terminology related to sex, gender, and family relationships is consistent with US Census data collection and reporting terminology, and may not reflect the terminology used by readers.) Extended families: The extended family can be very complex. It includes two or more family units functioning as a single integrated family. It may involve three or more generations (e.g., grandparents, parents, and children), polygamous families with multiple spouses and their offspring, or married siblings living together with their children, a type of extended family known as joint families. The extended family can be an effective social and economic unit because it involves multiple adults able to contribute to the household. Extended families have been most commonly associated with agricultural societies, where a high value is typically placed on labor and self-subsistence. In the United States today, we commonly see the emergence of the extended family during times of transition, such as when family members are changing jobs, returning to school, or recovering from economic hardship. Worldwide, the extended family is the most common type of family. Figure 11.6 An extended family in Pretoria, South Africa, including several generations. A family functions as a combined socioeconomic unit, where family members cooperate and support each other within the same household. (credit: Henry M. Trotter/Wikimedia Commons, Public Domain) Blended families: Blended families are families in which there is more than one origin point for the members. This typically occurs when one or more divorced and/or widowed adults with children remarry, combining two formerly independent units into a new blended family. Blended families are common in the United States and in societies in which we find serial monogamy. Although the US census does not collect data specifically on stepfamilies, in 2009 Pew Research estimated that 16 percent of all American children lived in blended families.