Endogamy
Endogamy is the practice of
marrying within a social group because of social norms that encourage or require it. An example of endogamy is that practiced by the tribes of
Iraq. Because tribal membership is determined by patralineal lines, a woman who marries outside a tribe leaves that tribe. As a result, marriage between cousins or second cousins is frequent and encouraged.
The opposite of endogamy is exogamy.
See also incest.