A caste is a fixed social group into which an individual is born within a particular system of social stratification: a caste system. Within such a system, individuals are expected to: marry exclusively within the same caste (endogamy), follow lifestyles often linked to a particular occupation, hold a ritual status observed within a hierarchy, and interact with others based on cultural notions of exclusion, with certain castes considered as either more pure or more polluted than others. Its paradigmatic ethnographic example is the division of India's Hindu society into rigid social groups, with roots in south Asia's ancient history and persisting to the present time. However, the economic significance of the caste system in India has been declining as a result of urbanisation and affirmative action programs. A subject of much scholarship by sociologists and anthropologists, the Hindu caste system is sometimes used as an analogical basis for the study of caste-like social divisions existing outside Hinduism and India. The term "caste" is also applied to morphological groupings in eusocial insects such as ants, bees, and termites.