The relationship between parent and offspring is only one type of intimate association between living organisms observed in nature. Infants, parasites, symbiotes: all participate in relationships characterized by metabolic dependence between participants. This multiplicity of naturally occurring dependent relationships is useful in the study of parental behavior because an analysis of one type of intimate association can provide insight into others. For example, viewing the developing mammal as a parasite of its mother1, as a metabolically dependent active exploiter of its dam, can suggest ways of analyzing parent-offspring relationships not apparent from more traditional perspectives (Galef, 1981).