Among the two forms of polygamy, polygyny is by far the most widespread. Several different schemes have been proposed it explain its incidence. Some people suspect that a desire for numerous sex partners is built into basic human biology, a factor that would explain the almost its universal occurrence, but not the exceptions or variations. Other theories based on population and ecological factors explain it as a response lengthy periods of sexual abstinence that women must follow after child birth in some cultures. This practice reduces population growth, but drives husbands to acquire additional wives to meet unfulfilled sexual needs. Demographic theory suggests that polygyny may occur because of a surplus of women that results from a high incidence of male warfare. However, polygyny occurs in many situations of relatively balanced gender ratios or even, as in the case of the Yanomamo, where males outnumber females. Accordingly, some men accumulate two or more wives only at the expense of others who never marry, or, much more usually, marry at a later age than women do. As such, the society becomes divided between young bachelors, who may remain single into their thirties and older polygynists. This arrangement may occur informally or may become a marked feature of the social structure. For example, in some South African societies, such as the Zulu, all young men in their twenties were organized into military “age regiments” and were not allowed to marry until their term of service ended. As we have already suggested, differences in marital age are also created by bride wealth requirements.
The social division between polygynists and bachelors points to another
prevalent theory of polygyny, which is based on social stratification. In societies where men are not distinguished by differences in access to productive resources, such as land and capital, status distinctions are mainly attained and expressed through direct control over people. This goal is most obviously acheived through incorporating many women into one’s domestic group and expanding it by fathering a large number of children. Traditional South African marriage structures again provide an appropriate example. Most societies were divided into commoner, noble, and royal strata. Commoners usually were able to marry only one wife, nobles supported several, and royals could boast numbers that reached over a hundred. A stratificational theory of polygyny also accounts for its greater incidence in comparison to
polyandry, since men tend to occupy higher statuses than women in the majority of societies.