CHANGES IN THE AGGRESSIVENESS OF MICE RESULTING FROM SELECTIVE BREEDING, LEARNING AND SOCIAL ISOLATION

LAGERSPETZ, K. M. J. & LAGERSPETZ, K. Y. H. Changes in the aggressiveness of mice resulting from selective breeding, learning and social isolation. Scand. J. Psychol. 1971, 12, 241–248.–Selective breeding for aggressiveness and non‐aggressiveness in mice has now been going on for 19 generations. The aggressiveness score distributions of the males have not changed since the 7th generation. Socially naive male mice which had been living in isolation, had five encounters with submissive males, and five with receptive females. Learning of aggressive and sexual behaviour occurred in males of both the aggressive and the non‐aggessive strain. When living in groups, the males of both strains show no aggressiveness towards a submissive opponent. Social isolation for 1–2 weeks greatly increases the aggressiveness level of the animals of the aggressive strain. The effects of grouping is interpreted as social learning of non‐aggressive behaviour, the effect of isolation as return of the inter‐individually variable aggressiveness level, determined by genetic variation and early experience. Some neurochemical findings are in agreement with the observed behavioural effects.