nursing in infants and modulates their activity levels (Hofer, 1978). The basic requirements for food and warmth are universally recognized and are routinely met in the laboratory when contact with the mother is not possible.

Beyond those basic needs, the young of many mammalian species require stimulation from conspecifics, or from appropriate social substitutes, to ensure normal behavioral development and adult social competence (Newton and Levine, 1968). Although there is no question that the behavior of animals deprived of such stimulation from birth is atypical, it has not been established that they are chronically stressed. However, the behavior of many adult animals deprived of social interaction in early life is obviously maladaptive. Self-mutilation, hair-pulling, stereotypic behaviors, extreme timidity or aggressiveness, and inability to mate or provide adequate care to offspring are examples of maladaptive behaviors that might result from social deprivation and be taken as de facto evidence of distress. A concern with the well-being of captive animals and with their long-range utility for research and reproduction warrants provision of opportunities for social interaction of developing animals with members of their own species and in some cases with humans (e.g., in the case of dogs), unless deprivation of such opportunities is a carefully articulated requirement for a specific research project.

Disruption of infant-parent bonds: Given the opportunity, the young of some avian and mammalian species will form an emotional bond or attachment to their mother or an appropriate substitute. In those species, social deprivation occurs if an immature animal that has formed such a bond is separated from its attachment figure (Reite and Field, 1985). The acute responses indicate stress. Whimpering and other high-pitched vocalizations typically increase and are accompanied by corresponding changes in general activity, heart rate, and cortisol concentrations. Those reactions are adaptive under natural circumstances, in that they attract caregivers and prepare a young animal for vigorous action. If prolonged, however, they can become distressful and lead to increased vulnerability to disease. Distress is likely to be less intense and persistent in animals that no longer depend entirely on an attachment figure for nutritional and emotional support, that have access to familiar companions or a substitute attachment figure, and that remain in familiar surroundings after separation.

In some species, such as primates, mothers also show an emotional response to separation from their infants. Their behavioral and physiologic reactions appear to be similar to those of an infant, although less persistent and intense.

Disruption of adult bonds: The term social deprivation can also be applied to adult animals that are separated from familiar companions. The question of whether social bonds or emotional attachments that develop between adults are similar in form or intensity to attachments between parent and young has seldom been examined systematically. On the basis of comparisons between two primate species, one monogamous and the other polygamous, it appears that pair-living monogamous adults respond to separation in a manner that is similar to, but less intense and prolonged than, the response of immature animals to separation from an



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