governments Tribes are therefore considered to be a political unit formed from an organisation of families (including clans and lineages) based on social or ideological solidarity. Membership of a tribe may be understood as being based on factors such as kinship ("clan"), ethnicity ("race"), language, dwelling place, political group, religious beliefs, oral tradition and/or cultural practices. Archaeologists continue to explore the development of pre-state tribes. Current research suggests that tribal structures constituted one type of adaptation to situations providing plentiful yet unpredictable resources. Such structures proved flexible enough to coordinate production and distribution of food in times of scarcity, without limiting or constraining people during times of surplus. anthropologist Morton Fried argued in 1967 that bands organized into tribes in order to resist the violence and exploitation of early kingdoms and states. He wrote: Controversy and usage deprecation The term "tribe" was in common use in the field of anthropology until the late 1950s and 1960s. The continued use of the term has attracted controversy among anthropologists and other academics active in the social sciences, with scholars of anthropological and ethnohistorical research challenging the utility of the concept. In 1970, anthropologist J. Clyde Mitchell wrote: The tribe, a long respected category of analysis in anthropology, has recently been the object of some scrutiny by anthropologists ... Doubts about the utility of the tribe as an analytical category have almost certainly arisen out of the rapid involvement of peoples, even in the remotest parts of the globe, in political, economic and sometimes direct social relationship with industrial nations. The doubts, however, are based ultimately on the definition and meaning which different scholars give to the term 'tribe', its adjective 'tribal', and its abstract form 'tribalism'. Despite the membership boundaries for a tribe being conceptually simple, in reality they are often vague and subject to change over time. In his 1975 study, The Notion of the Tribe, Fried provided numerous examples of tribes that encompassed members who spoke different languages and practiced different rituals, or who shared languages and rituals with members of other tribes. Similarly, he provided examples of tribes in which people followed different political leaders, or followed the same leaders as members of other tribes. He concluded that tribes in general are characterized by fluid boundaries, heterogeneity and dynamism, and are not parochial. Part of the difficulty with the term is that it seeks to construct and apply a