↑People, James; Bailey, Garrick (2010). Humanity: An Introduction to Cultural Anthropology (9th ed.). Wadsworth Cengage learning. p. 389. In essence, an ethnic group is a named social category of people based on perceptions of shared social experience or ancestry. Members of the ethnic group see themselves as sharing cultural traditions and history that distinguish them from other groups. Ethnic group identity has a strong psychological or emotional component that divides the people of the world into opposing categories of “us” and “them.” In contrast to social stratification, which divides and unifies people along a series of horizontal axes on the basis of socioeconomic factors, ethnic identities divide and unify people along a series of vertical axes. Thus, ethnic groups, at least theoretically, cut across socioeconomic class differences, drawing members from all strata of the population.