A race is a categorization of humans based on shared physical or social qualities into groups generally viewed as distinct within a given society. The term came into common usage during the 16th century, when it was used to refer to groups of various kinds, including those characterized by close kinship relations. By the 17th century, the term began to refer to physical (phenotypical) traits, and then later to national affiliations. Modern science regards race as a social construct, an identity which is assigned based on rules made by society. While partly based on physical similarities within groups, race does not have an inherent physical or biological meaning. The concept of race is foundational to racism, the belief that humans can be divided based on the superiority of one race over another. Social conceptions and groupings of races have varied over time, often involving folk taxonomies that define essential types of individuals based on perceived traits. Today, scientists consider such biological essentialism obsolete, and generally discourage racial explanations for collective differentiation in both physical and behavioral traits. Even though there is a broad scientific agreement that essentialist and typological conceptions of race are untenable, scientists around the world continue to conceptualize race in widely differing ways. While some researchers continue to use the concept of race to make distinctions among fuzzy sets of traits or observable differences in behavior, others in the scientific community suggest that the idea of race is inherently naive or simplistic. Still others argue that, among humans, race has no taxonomic significance because all living humans belong to the same subspecies, Homo sapiens sapiens. Since the second half of the 20th century, race has been associated with discredited theories of scientific racism, and has become increasingly seen as a largely pseudoscientific system of classification. Although still used in general contexts, race has often been replaced by less ambiguous and/or loaded terms: populations, people(s), ethnic groups, or communities, depending on context. Defining race Modern scholarship views racial categories as socially constructed, that is, race is not intrinsic to human beings but rather an identity created, often by socially dominant groups, to establish meaning in a social context. Different cultures define different racial groups, often focused on the largest groups of social relevance, and these definitions can change over time. In South Africa, the Population Registration Act, 1950 recognized only White, Black, and Coloured, with Indians added later.