Cross-cultural patterns of marriage. Considerations given at marriage. Cross-cultural patterns of marriage. Often this is fraternal polyandry and the younger brother leaves when he can accommodate a wife of his own. At a given time, most marriages are probably of this type, because it includes most marriages in societies which allow polygyny, but in which it is only practiced occasionally.
Marriage is fundamentally a reproductive union.
There are many exceptions, but cross culturally it forms the basis for reproductive unions and legitimizing offspring. Many anthropologists disagree and say it is an economic union because most of what married couples do cooperatively is not directly related to reproduction. This disregards the larger evolutionary context of mating systems. But they ultimately serve reproductive ends. You could not understand the union without understanding this.