ABSTRACT
This chapter introduces W. D. Hamilton’s rule—the technical formulation of inclusive fitness theory. It argues that favoritism that parents show their own children is a special case of favoritism toward the “vehicles” that contain copies of their genes. The chapter explores the profound consequences of this formulation for topics such as cooperation, conflict, risk taking, inheritance of wealth, and grieving. It explains the theory of inclusive fitness and provides several empirical examples that illustrate the importance of genetic relatedness for helping. The chapter describes two studies that suggest that genetic relatives make a difference between life and death. It analyzes why maternal grandmothers would invest more than paternal grandfathers in their grandkids. The chapter explains from an evolutionary perspective, why families might form. Anthropologists, in contrast, tend to stress kinship, defining families as groups of parents, unmarried children, and sometimes extended kin through which lines of descent can be traced.
