Cousin marriage is marriage between people with a common grandparent or between people who share another relatively recent ancestor. Such marriages range from being considered ideal and actively encouraged, to being uncommon but still legal, to being seen as incestuous and legally prohibited. Although now stigmatized in the Western world, they remain relatively common in the Middle East, where, in some nations, they account for over half of all marriages. Worldwide, over one in every ten marriages are between first and second cousins.One type of cousin marriage which has been allowed in many cultures is cross-cousin marriage. This kind was common among aboriginal tribes in Australia, North America, South America and Polynesian tribes in the past. Various religions have ranged from prohibiting sixth cousins or closer from marrying to freely allowing first-cousin marriage. Cousin marriage is an important topic in anthropology and alliance theory.Children of first-cousin marriages have a doubled risk of genetic disorders (although scientists contend this is relatively small, at six percent, compared with a three percent risk for children whose parents are not genetically related to each other). Supporters of cousin marriage in the West may view legal bans as discrimination, while opponents may appeal to moral or other arguments.