Monogamy, the union between two individuals, is the most common form of marriage. While monogamy traditionally referred to the union of one man and one woman, there are some countries that recognize same-sex unions. As of early 2015, The Netherlands, Spain, Canada, South Africa, Norway, Sweden, Portugal, Iceland, Argentina, Denmark, Brazil, France, Uruguay,
New Zealand, the United Kingdom, Luxembourg, and Finland legally allow same-sex marriage. In other countries, the debate continues over whether or not to legalize same-sex marriage or guarantee rights to homosexuals. For instance, certain states in Mexico allow same-sex marriage, but not the entire nation. Serial monogamy, where an individual has multiple spouses over their lifetime, but only one at a time, is quite common in industrial societies.
Polygamy, the union between three or more individuals is the second most common form of marriage. Generally when polygamy is mentioned by the media, a marriage between a man and multiple women is being referenced; however, the term is being misused.
Polygyny is the correct term for a marriage between a man and multiple women. Polyandry refers to a marriage between a woman and multiple men. Polyandry mostly occurs between a woman and brothers, a system referred to as fraternal polyandry.
One reason that polyandry might be the preferred marriage pattern for a group is if there is a shortage of women or land is scarce. For instance, the Nyinba of Nepal practice fraternal polyandry because there is not enough land to divide between brothers and the high mortality rate of female child and infant mortality. Male children are preferred, therefore are better cared for then female offspring (Bonvillain 2010: 218-219).
