Abstract
The present experiment was conducted to investigate changes in social behaviors in two groups of isolation-reared infant japanese monkeys. Each group, one is early-isolation group and the other late-isolation group, consisted of three one-year-old infants (Table 1). The dominant-subordinate ranking among the infants during the daily short-term period of group formation was unstable and reversed in the early-isolation group (Fig. 1, 2), while it was established smoothly and was stable in the late-isolation group (Fig. 3, 4). The dominant-subordinate ranking in the early-isolation group, however, became stable through the monthly long-term period of group formation.
These differences between the two groups seemed to be due to the difference in social rearing condition and emotional stabilities in the infants. As a result of prolonged social experiences the occurrence of dominant behaviors such as approach, grasp and threat decreased and tended to become averaged in the two groups. Furthermore, elaborate social behaviors such as social play and social grooming appeared in the two groups (Fig. 5, 6).
The appearances of these behaviors might indicate elevation of sociality of the infants in each group. The elevation in sociality was correlated more with the dominant-subordinate ranking than with the age of the isolation of the infants. Thus, the prolonged social experiences seemed to give rehabilitating effects upon sociality of these isolation-reared infants.
The present results differ from those described by Suomi, S. J. (1972) in that our isolates showed marked recovery in social behaviors in spite of the absence of interaction with socially normal monkeys younger than themselves.
There was a high correlation between the dominant-subordinate ranking and the occurrences of the environmental contacts (Fig. 7). Consequently, it may be predicted that an infant who acts highly upon environment will be dominant in future.
