Polygamy (specifically polygyny, where one man has multiple wives) has been practiced in many tribal societies for various reasons. Three main causes are:
Economic Factors: In subsistence-based tribal economies, having more family members means a larger workforce. More wives and children can contribute to agricultural work, animal husbandry, and domestic chores, thereby increasing the economic productivity and wealth of the household.
Social Status and Prestige: In many tribal cultures, the number of wives a man has is a direct indicator of his social status, wealth, and power within the community. It is a mark of prestige and influence.
Demographic and Social Customs:
A surplus of women over men in the marriageable age group can sometimes lead to polygyny.
The custom of levirate, where a man is obligated to marry his deceased brother's widow to support her and her children, can also result in polygynous marriages.
The desire for a male heir can also be a cause, where a man takes a second wife if the first wife does not produce a son.