This chapter examines characterizations and explanations of parental investment strategies in forager, farmer, and urban-industrial cultures. P. Draper and H. Harpending were among the first to explain differences in parental investment using evolutionary theory. The applicability of the models is explored by examining parent-infant interactions in three populations: Aka foragers and Ngandu farmers of the Central African Republic and upper-middle-class Euro-Americans from Washington, D.C. Aka are primarily foragers and Ngandu predominantly farmers, all Aka today farm at least part of the year and most Ngandu, men in particular, spend part of the year in the forest hunting or gathering forest products. Most of the Ngandu men and several of the Ngandu women had an elementary education. The Aka and Ngandu live in the tropical rainforest, have similar mortality and fertility patterns, and see each other's parenting patterns on a regular basis. Ngandu sharing is less frequent and extensive than among the Aka, in part because living conditions are less intimate.