A widespread marriage practice is the regulation of whether a partner comes from outside or inside one’s own kin group or community. The rule of exogamy requires that the marriage partner come from outside one’s own kin group or community. Exogamy can take many forms. It may mean marrying outside a particular group of kin or outside a particular village or group of villages. Often, then, spouses come from a distance. For example, in Rani Khera, a village in India, 266 married women originally came from some 200 different villages that were, on average, between 12 and 24 miles away. Meanwhile, 220 local women had gone to 200 other villages to marry. As a result of these exogamous marriages, Rani Khera, a village of 150 households, was linked to 400 other nearby villages.75 When there are rules of exogamy, violations are often believed to cause harm. On the islands of Yap in Micronesia, people who are related through women are referred to as “people of one belly.” The elders say that if two people from the same kinship group married, they would not have any female children and the group would die out.76
People in exogamous societies with very low population densities often have to travel considerable distances to meet mates. A study of foragers and horticulturalists found a clear relationship between population density and the distance between the communities of the husband and wife—the lower the density, the greater the marriage distance. Because forager societies generally have lower population densities than horticulturalists, they generally have further to go to find mates. Among the !Kung, for instance, the average husband and wife had lived 40 miles (65 kilometers) from each other before they were married.77
The opposite rule, endogamy, obliges a person to marry within a particular group. The caste groups of India traditionally have been endogamous. The higher castes believed that marriage with lower castes would “pollute” them, and such unions were forbidden. Caste endogamy is also found in some parts of Africa. In East Africa, a Masai warrior would never stoop to marry the daughter of an ironworker, nor would a former ruling-caste Tutsi in Rwanda, in central Africa, think of marrying a person from the hunting caste Twa.