Abstract
This report was primarily concerned with the comparison of aggressivity in isolation-reared adult Japanese monkeys of various rearing conditions in the pairing experiment with strangers. Results for the males indicate that they were extremely aggressive to strange partners, and that their aggressivity was negatively correlated to the severity of their isolation (Table 1, Fig.1). According to the high frequencies of discreteness between the isolates and their partners (Fig. 2) and the remarkable tendency of the aggressees' withdrawal (Table 2), their aggression may be regarded as repulsive behavior directed to the strangers.
Because of the poverty of social experience, the strange partners were more novel for the isolates than for the controls, and so fear produced by the strangers' novelty may be thought as the cause of their aggression. However, the fact that the isolates rarely showed non-defensive aggression when they were subordinate to the partner (Fig. 1) indicates that excessive fear does not result in aggression. In other words, “moderate” level of fear causes aggression. On the other hand, occurrence of aggression also requires “primary” sociability which enables individuals to approach and contact with others, and this appears to be the main reason why the less severely isolated monkeys aggressed more. To summarize above, their aggressivity may be influenced by a level of fear and of “primary” sociability.
The isolates lack the more mature form of sociability, that is, “friendly” sociability which can act as an inhibitor of their aggression, and for that reason they showed their aggressivity in a less inhibited fashion.
In contrast to the males, the females rarely showed aggressive behavior except F-3 (Fig. 1). The severely isolated females were hyperfearful (Table 2), and the least severely isolated female was even friendly. This can be attributed to sex difference in which females tend to be more friendly, more fearful, and less aggressive than males.
