parental investment theory
the proposition that many sex differences in sexually reproducing species (including humans) can be understood in terms of the amount of time, energy, and risk to their own survival that males and females put into parenting versus mating (including the seeking, attaining, and maintaining of a mate). Differences in parenting and mating investment between males and females vary among species and as a function of environmental conditions. [proposed in 1972 by U.S. sociobiologist Robert L. Trivers (1943– )]