Marriage is a fundamental practice that influences village dynamics and political processes in many societies in past and present human cultures. Not only is marriage a process that supports human kinship systems, it allows for alliances and reciprocity systems between groups that create variation in human social organization (Walker et al. 2011). This paper explores the sources of variation in marriage and mating systems in two very different societies, the !Kung San and the Yanomamo, in terms of the vastly different environments each of them inhabit. The !Kung San, a traditional nomadic hunter-gatherer society, reside in the Dobe area on the edge of the Kalahari desert of Botswana (Shostak 1981, p.7). Due to the demanding environment of
2011).

Another major variation between the Yanomamo and the !Kung San in marriage and mating systems is in polygyny and monogamy. Serial monogamy is the most common form of marriage system among the !Kung, although infidelity is common and polygynous unions can be observed (Shostak 1981, p. 151-153). In environments where resources are scare, the rate of infant mortality and inter-birth intervals (IBI) tends to be greater, as demonstrated in !Kung society with an infant mortality rate of 20% in the first year and an IBI of approximately 4 years (Shostak 1981, p. 79-60, 152; Jones 1986). This increase in mortality leads to the increased demand for parental care and resources to ensure the survival of children to reproductive age, ensuring their genes are passed to subsequent generation and increasing fitness (Hames 1996). If a male engages in a polygynous union, paternal childcare and resources attained are divided between the offspring produced by both wives, thus decreasing parental care and the chance of survival of all offspring produced (Hames 1996). However, in monogamous unions, resources attained by husbands, are