<P> Matrilateral cross-cousin marriage has been found by some anthropological researchers to be correlated with patripotestal jural authority, meaning rights or obligations of the father . According to some theories, in these kinship systems a man marries his matrilateral cross-cousin due to associating her with his nurturant mother . Due to this association, possibly reinforced by personal interaction with a specific cousin, he may become "fond" of her, rendering the relationship "sentimentally appropriate". Interestingly, patrilateral cross-cousin marriage is the rarest of all types of cousin marriage, and there is some question as to whether it even exists . </P> <P> In contrast to Lévi - Strauss who viewed the exchange of women under matrilateral cross-cousin marriage as fundamentally egalitarian, anthropologist Edmund Leach held that such systems by nature created groups of junior and senior status and were part of the political structure of society . Under Leach's model, in systems where this form of marriage segregates descent groups into wife - givers and wife - takers, the social status of the two categories also cannot be determined by a priori arguments . Groups like the Kachin exhibiting matrilateral cross-cousin marriage do not exchange women in circular structures; where such structures do exist they are unstable . Moreover, the exchanging groups are not major segments of the society, but rather local descent groups from the same or closely neighboring communities . Lévi - Strauss held that women were always exchanged for some "prestation" which could either be other women or labor and material goods . Leach agreed but added that prestations could also take the form of intangible assets like "prestige" or "status" that might belong to either wife - givers or wife - takers . </P> <P> Anthropologists Robert Murphy and Leonard Kasdan describe preferential parallel cousin marriage as leading to social fission, in the sense that "feud and fission are not at all dysfunctional factors but are necessary to the persistence and viability of Bedoin society". Their thesis is the converse of Fredrik Barth's, who describes the fission as leading to the cousin marriage . Per Murphy and Kasdan, the Arab system of parallel cousin marriage works against the creation of homogenous "bounded" and "corporate" kin groups and instead creates arrangements where every person is related by blood to a wide variety of people, with the degree of relationship falling off gradually as opposed to suddenly . Instead of corporate units, Arab society is described as having "agnatic sections", a kind of repeating fractal structure in which authority is normally weak at all levels but capable of being activated at the required level in times of war . They relate this to an old Arab proverb: "Myself against my brother; my brother and I against my cousin; my cousin, my brother and I against the outsider ." "In such a society even the presence of a limited amount of cross-cousin marriage will not break the isolation of the kin group, for first cross cousins often end up being second parallel cousins ." Instead of organizing horizontally through affinal ties, when large scale organization is necessary it is accomplished vertically, by reckoning distance from shared ancestors . This practice is said to possess advantages such as resilience and adaptability in the face of adversity . </P> <P> A recent research study of 70 nations has found a statistically significant negative correlation between consanguineous kinship networks and democracy . The authors note that other factors, such as restricted genetic conditions, may also explain this relationship . This follows a 2003 Steve Sailer essay published for The American Conservative, where he claimed that high rates of cousin marriage play an important role in discouraging political democracy . Sailer believes that because families practicing cousin marriage are more related to one another than otherwise, their feelings of family loyalty tend to be unusually intense, fostering nepotism . </P>

When did it become legal for first cousins to marry