Animal Family

Cousins of an older generation (in other words, one's parents' first cousins), although technically first cousins once removed, are often classified with "aunts" and "uncles." Similarly, a person may refer to close friends of one's parents as "aunt" or "uncle," or may refer to close friends as "brother" or "sister," using the practice of fictive kinship. English-speakers mark relationships by marriage (except for wife/husband) with the tag "-in-law." The mother and father of one's spouse become one's mother-in-law and father-in-law; the female spouse of one's child becomes one's daughter-in-law and the male spouse of one's child becomes one's son-in-law. The term "sister-in-law" refers to three essentially different relationships, either the wife of one's sibling, or the sister of one's spouse, or, in some uses, the wife of one's spouse's sibling. "Brother-in-law" expresses a similar ambiguity. No special terms exist for the rest of one's spouse's family. The terms "half-brother" and "half-sister" indicate siblings who share only one biological or adoptive parent.
Economic functions
Anthropologists have often supposed that the family in a traditional society forms the primary economic unit. This economic role has gradually diminished in modern times, and in societies like the United States it has become much smaller, except in certain sectors such as agriculture and in a few upper class families. In China the family as an economic unit still plays a strong role in the countryside. However, the relations between the economic role of the family, its socio-economic mode of production and cultural values remain highly complex.