Arable land, land available for agriculture, is an important indicator of a region's resources, especially in pre-industrial societies. The number of adults and offspring that are able to live in one family unit is greatly dependent on the quantity of resources available and how difficult it is to acquire them. Because of this, different regional topographies influence the social norms for marriage seen in different human populations across the world.
Polygyny - One Husband, Multiple WivesHistorically, the large majority of human societies prefer polygynous marriage as a cultural ideal. In fact, data from hundreds of studied human societies show that about 84% were polygynous, 16% were monogamous, and less than half a percent were polyandrous. Polygyny has existed on all inhabited continents in a wide variety of ecosystems, provided there were enough resources to support the additional wives and children.
Polygyny is the default structural framework for marriage in human societies, while monogamy and polyandry appeared to arise in pre-industrial societies as a response to environmental scarcity. Mormonism famously adopted and encouraged polygamy among its followers, as polygyny is the most efficient way for a man to sire as many offspring as possible. Sephardic Jews (of Spanish heritage) were known to practice polygyny as late as the fourteenth century.
In societies with constant shortages of men, polygyny was seen as the best solution to insure that all women could get married. For example, in many societies war between neighboring clans or groups was relatively constant, resulting in a skewed adult sex ratio. With an overabundance of females, polygyny was seen as the most viable solution.
Of course, in societies where the sex ratio was roughly equal, some men would have multiple wives while others would not be able to marry at all, causing serious societal issues and discontent.
Monogamy - One Husband and One WifeIn societies where arable land was scarce, monogamy was often employed as the most effective reproductive strategy for creating the next generation. For example, in pre-industrial Europe, most lived in the countryside on farms. Peasants lived under a feudal system where one family worked a plot of land just large enough to support a family, generally much smaller than a polygynous family. Most if not all usable farming land was claimed, making in extremely difficult or practically impossible to expand one family's farmland.
In inheritance, the land could not be divided between multiple sons because the subsequent divided plots would be too small to support a family of any size. Thus, all farmland in a family was passed down to the eldest son who then had enough resources to marry one wife and provide for a family. The subsequent sons filled other positions in society, for example as soldiers or priests, often remaining unmarried.
In this society, due to the scarcity of arable land, the social position of being a wife to a farmer became a scarce resource. This caused stiff competition between European women. To make their daughters more attractive prospects for marriage, families began to pay dowries to the groom. Women who were unable to marry filled other societal niches, for example by becoming spinsters, prostitutes, or nuns.
Thus, out of necessity, monogamy became characteristic of pre-industrial societies where there was a considerable scarcity of land.
Polyandry - One Wife, Multiple HusbandsPolyandry is very rarely found in human societies, but nevertheless is still present to a very minor extent in some modern-day cultures found in Tibet, Nepal, and India, although in many cases the government has outlawed the practice.
Polyandrous cultures generally are found in environments where arable land is not only scarce but also extremely difficult and laborious to farm, such as rocky mountain terrain. Because the land is so work-intensive to farm, several men are necessary on each family farm in order for the plot to be able to support one family.
The land is not capable of providing for many; if each male had separate wives and children than they all would surely starve. Thus, out of necessity polyandry, or wife sharing, became a culturally acceptable reproductive strategy. Generally the men engaging in wife sharing are brothers so that the offspring produced are at least their nieces and nephews. Wife sharing between non-related husbands is exceedingly uncommon, but has been reported to occur.
Of course, the quality and quantity of arable land accessible to a society is by no means the only variable determining whether a society is more likely to be polygamous or not. In fact, the modern movement for monogamy in the Western world for the last few centuries was largely fueled by the want of Roman cultural ideals by the Roman Catholic Church. Nonetheless, it is undeniable that there is a very unique and interesting relationship between the geography of a region and how a culture defines marriage.
References:Kanazawa, S. (2008, June 5). Why are there virtually no polyandrous societies. Retrieved from http://www.psychologytoday.com/blog/the-scientific-fundamentalist/200806/why-are-there-virtually-no-polyandrous-society-0
The Jewish Encyclopedia: Polygamy. (n.d.). Retrieved from http://www.jewishencyclopedia.com/articles/12260-polygamy