19.6 Describe the three different rules regarding how many persons one can marry, and explain social or economic reasons for each.
Today, in most Western societies, monogamy, not only is the form of marriage in which one has only one spouse at a time (usually one man and one woman) customary, but plural marriage is illegal. However, cross-culturally, most societies known to anthropology have allowed some form of polygamy, or plural spouse marriage. There are two types of polygamy. Polygyny, the form of marriage that allows a man to be married to more than one woman at the same time, is very common. The mirror image of polygyny, the marriage of one woman to more than one man at the same time, is called polyandry. It is practiced in just a few societies. However, societies with polygamy cannot practice it exclusively because few, if any, societies have twice as many of one gender than the other. So in a polygynous society, for example, most men will be married monogamously at any given time. Group marriage, in which more than one man is married to more than one woman at the same time, sometimes occurs but is not customary in any known society.