the postulation that several carnal variants in sexually reproducing species can be comprehended with regard to the quantity of time, energy and risk to their own survival which females and males invest in mothering or fathering versus mating. Variants in mothering or fathering and mating investment between females and males vary across species and as an operative of surrounding conditions.

PARENTAL INVESTMENT THEORY: "Today in class, we are going to discuss the parental investment theory and how it applies to each student's upbringing."