EFFECTS OF SEPARATION FROM MOTHER ON THE EMOTIONAL BEHAVIOR OF INFANT MONKEYS

After studying emotion for more than 30 years, P. T. Young wrote, “A developmental view of the organism is ordinarily needed to recognize and name emotions consistently. ” (Young, 1961, p. 41 1 ) . In our laboratory we have studied emotional behavior within a developmental context, first by noting its speciestypical ontogeny under relatively undisturbed conditions, and then by studying the reactions of young infants when they were bereft of their mothers by our design. For six years we have been studying numerous groups of two species of macaque, pigtails (Macaca nernestrina) and bonnets (Macaca radiata) . Each group consists of a wild-born adult male, four or five wild-born adult females, and their laboratory-born offspring. To date, more than 60 infants have been born, of whom 57 are living. Some mothers have had four or five offspring, with whom they still live together in their original groups. During systematic observations (Kaufman & Rosenblum, 1966) of the various groups, we were impressed by a marked difference between these closely related species in their tendency toward physical closeness with neighbors (Rosenblum et al., 1964). In bonnet groups, adult members spend many hours in close passive contact with each other, often in huddles (FIGURE 1 ) , whereas pigtail adults usually do not make physical contact (FIGURE 2) except to engage in a more dynamic social interaction such as mating, grooming, or fighting. This species difference appeared rapidly when groups were first formed, and was not altered appreciably by food deprivation (Rosenblum et al., in press) or by systematic changes in the ambient temperature between 72’ and 8 8 O F. More relevant to this paper is the fact that bonnet females remain in close physical contact with each other even after the birth of infants (FIGURE 3 ) , whereas pigtail mothers with infants tend to remain apart from other females (FIGURE 4 ) . This consistent and statistically significant difference in spatial propinquity between the species appears to reflect a significant character of the basic structure of their social behavior, as it may be seen in the behavior of the mother-infant dyad and the development of the young (Rosenblum & Kaufman, 1967; Kaufman & Rosenblum, in press a) . Bonnet mothers are more relaxed about their infants than pigtail mothers: they permit them more interaction with others; they guard, restrain, and retrieve the infants less (FIGURE 5); they wean less; and they punish less (FIGURE 6). Bonnet infants, accordingly, show differences from pigtails in their development that seem to include emotional differences. They appear to be more secure: they are less dependent on their mothers in that they go away from them more often, for further distances, and for longer periods; they are freer to approach other members of the group, both adults and peers; and they spend more time in social play, whereas pigtail infants spend more time in isolated play, although the total amount of play is similar in the two species. We may see here a mechanism of great importance in the perpetuation of the species-characteristic difference in spatial patterning and temperament.