more usual to use the local divorce system to terminate the relationship. Consanguinity In Christian cultures, the Biblical proscriptions contained in Leviticus 18 v6–18, are used as the basis for restricting marriage between persons who are deemed to be too closely related to each other. More generally, the restrictions fall into two classes (and based on Old Testament laws): where the parties are related by blood (consanguinity); or where parties are related by marriage (affinity). Several exceptions have been described for various Biblical figures, incestuous relationships such as Abraham and Sarah, Nachor and Melcha, Lot and his Daughters, and Amram and Jochebed. The limitations based on consanguinity derive from a policy of practical eugenics and reflect the increased possibility that such marriages will produce children with a genetic defect due to the limitations on their combined gene pool. The limitations based on affinity, by contrast, are predominantly legal and social in origin. The rules relating to affinity reflect the need to minimise the prospects of familial jealousies and dysfunction by preventing the intermarriage of people already related by marriage. Difficult questions arise on whether an adopted child may marry his or her adoptive parents, or the natural children of the adoptive parents. No matter what legislative decisions are taken, there will always be citizens who wish to evade the application of the law. There will be no problem if they relocate and establish a matrimonial home in a state that allows their marriage. But any attempt to evade such laws by going through a ceremony in a state that permits the marriage and then returning to the original state (which will usually be their state of domicile, nationality or habitual residence) will fail, and may even expose the couple to the risk of prosecution for incest or an equivalent offense. Polygamy Polygamy may be polygyny (one man having more than one wife at the same time) or polyandry (one woman having more than one husband at the same time) and it has been practiced sparsely throughout history in almost all cultures and sanctioned by various religions where it was considered necessary to meet population or economic needs. In some economically poor areas where infant mortality is high but children are a vital source of labor to maintain the earning capacity of the family, polygamy may provide more children. States which prohibit polygamous marriages under national law often also criminalize bigamy.