Experimental programming of life histories: Toward an experimental science of individual differences

Abstract

Abstract Four experimental variables were combined in a 2 × 2 × 2 × 2 factorial design. These were ( 1 ) infantile handling vs. no handling of the mothers of the subjects, ( 2 ) infantile handling vs. no handling of the subjects, ( 3 )rearing of the subjects in either a maternity cage or a free environment between birth and weaning, and ( 4 ) rearing of the subjects in either a laboratory cage or a free environment between weaning and 42 days of age ( N = 6 Purdue‐Wistar rats per group). Starting at 220 days of age, the groups were given a battery of tests which measured emotional reactivity, exploratory behavior, and consumption‐elimination. Analysis of the criterion data revealed the following: ( 1 ) handling pups in infancy reduced emotional reactivity and this reduction was found to be invariant with respect to different combinations of life history experiences; ( 2 ) exploratory behavior was markedly influenced by the animal's pattern of life experiences; ( 3 ) when mothers were handled during their infancy, their offspring explored significantly less than offspring of nonhandled mothers.