Religious stratification is the division of a society into hierarchical layers on the basis of religious beliefs, affiliation, or faith practices. According to Kingsley Davis and Wilbert E. Moore, "[t]he reason why religion is necessary is apparently to be found in the fact that human society achieves its unity primarily through the possession by its members of certain ultimate values and ends in common". Furthermore, Davis and Moore contend that it is "the role of religious belief and ritual to supply and reinforce this appearance of reality" that these "certain ultimate values" have. This is one possible explanation for why religion is one of the underlying factors which links various forms of inequality into a chain of stratification. Critical overview Broadly defined, social stratification is constituted by the division of a society into hierarchical layers of wealth, power, and prestige. These layers, or strata, have been related to a variety of social categories, such as: Race Class Gender Ethnicity Religion Sociologists have paid attention to stratification based on race, class, gender, and ethnicity. Religion is closely tied to ethnic affiliation. Research suggests that religious stratification deserves more attention than it usually gets. It is a common development in religiously diverse societies. Once it becomes embedded in societies' laws, customs, and ideologies, it tends to persist. It also has societal consequences. Thus, it is important in its own right, but also in relation to other forms of stratification. In the United States Sociologists James D. Davidson and Ralph E. Pyle (2011) argue that religious stratification emerged during America's colonial period, as a result of religious ethnocentrism, religious competition, and unequal resources. They show that Anglicans, Congregationalists, and Presbyterians were over-represented among the economic, political, and educational elites. Other Protestant groups, Catholics, Jews, and people with no religious preference ranked much lower in status. The ranking of religious groups has changed in some ways over the course of U.S. history (Davidson and Pyle 2011, Pyle 1996). Most notably, Jews have risen into the upper stratum, while Catholics have climbed into the upper-middle stratum. However, religious stratification persists. For example, Anglicans (now Episcopalians), Congregationalists (now United Church of Christ), and Presbyterians remain in the upper stratum, and other Protestants groups such as Baptists (who ranked low in the colonial period) still have not experienced much upward mobility. These developments are linked to inter-religious power struggles related to membership size, organizational capacity, and resources.