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Abstract

The present series of studies intended to analize the occurrence of spontaneous individual differences in the behavioral performance of rodents. In experiment A we showed that in adult rats, the individual performances in each of four behaviors (burrowing, food hoarding, exploration and insect predation) differed markedly. In experiment B we studied the spontaneous development of such individual differences in young rats and found that already in weanling animals there are conspicuous performance differeces which accentuate as the animals grow older. In experiments C and D we showed that golden hamsters and mice also have individual differences in these four behaviors, although with characteristics that possibly are related to the social structure of the species. In experiments E and F we showed that individual differences in rats are not restricted to these four kinds of behavior. From these studies we conclude that behavioral individualization is a biological property with broad phylogenetic roots that occurs spontaneously and early in the animal's life and probably interrelates with the social organization of the species.