The diverse data coming from ethnography, history, law and social statistics, establish that the human family is an institution and not a biological fact founded on the natural relationship of consanguinity.
Early scholars of family history applied Darwin's biological theory of evolution in their theory of evolution of family systems. American anthropologist Lewis H. Morgan published Ancient Society in 1877 based on his theory of the three stages of human progress from Savagery through Barbarism to Civilization. Morgan's book was the "inspiration for Friedrich Engels' book" The Origin of the Family, Private Property and the State published in 1884.
Engels expanded Morgan's hypothesis that economical factors caused the transformation of primitive community into a class-divided society. Engels' theory of resource control, and later that of Karl Marx, was used to explain the cause and effect of change in family structure and function. The popularity of this theory was largely unmatched until the 1980s, when other sociological theories, most notably structural functionalism, gained acceptance.
In human context, a family (from Latin: familiare) is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children. Extended from the human "family unit" by biological-cultural affinity, marriage, economy, culture, tradition, honor, and friendship are concepts of family that are physical and metaphorical, or that grow increasingly inclusive extending to community, village, city, region, nationhood, global village and humanism. A family group consisting of a father, mother and their children is called a nuclear family. This term can be contrasted with an extended family.
There are also concepts of family that break with tradition within particular societies, or those that are transplanted via migration to flourish or else cease within their new societies. As a unit of socialization and a basic institution key to the structure of society, the family is the object of analysis for sociologists of the family. Genealogy is a field which aims to trace family lineages through history. In science, the term "family" has come to be used as a means to classify groups of objects as being closely and exclusively related. In the study of animals it has been found that many species form groups that have similarities to human "family"—often called "packs."
