Concept
A cousin marriage is a marriage where the spouses are cousins (i.e. people with common grandparents or people who share other fairly recent ancestors). The practice was common in earlier times and continues to be common in some societies today, though in some jurisdictions such marriages are prohibited. Worldwide, more than 10% of marriages are between first or second cousins. Cousin marriage is an important topic in anthropology and alliance theory. In some cultures and communities, cousin marriages are considered ideal and are actively encouraged and expected; in others, they are seen as incestuous and are subject to social stigma and taboo. Cousin marriage was historically practiced by indigenous cultures in Australia, North America, South America, and Polynesia. In some jurisdictions, cousin marriage is legally prohibited: for example, in mainland China, Taiwan, North Korea, South Korea, the Philippines, and 24 of the 50 United States. The laws of many jurisdictions set out the degree of consanguinity prohibited among sexual relations and marriage parties. Supporters of cousin marriage where it is banned may view the prohibition as discrimination, while opponents may appeal to moral or other arguments. Opinions vary widely as to the merits of the practice. Children of first-cousin marriages have an increased risk of autosomal recessive genetic disorders, and this risk is higher in populations that are already highly ethnically similar. Children of more distantly related cousins have less risk of these disorders, though still higher than the average population. A study indicated that between 1800 and 1965 in Iceland, more children and grandchildren were produced from marriages between third or fourth cousins (people with common great-great- or great-great-great-grandparents) than from other degrees of separation. The prevalence of first-cousin marriage in Western countries has declined since the late 19th century and early 20th century. In the Middle East and South Asia, cousin marriage is still strongly favored.