ABSTRACT
The reproductive interests of all adults are more or less similar in the household of an exclusively monogamous couple consisting of their children and one or more non-reproductive grandparents who have no other children. An important result of our analysis is that it provides a possible explanation for a paradox that has threatened to undermine the application of evolutionary theory to human behavior. Economics has tended to emphasize the important role of human cooperation, while evolutionary biology has tended to emphasize conflict. By joining economics with biology hope to strike a proper balance. In terms of theoretical models of human behavior, the theory of extended fitness has two major advantages: it is simple and it is powerful. Ever since John Locke, the Western tradition of political philosophy has emphasized the importance of property as a cornerstone of the social contract between individuals and their governments.
