CHIMPANZEES reared in total social isolation developed abnormal bcha\-iour patterns sucli as stereotyped movements, head-banging and digit-sucking (Davenport and Menzel, 1963). Isolation experiments with rliesus monkeys have shown, similar results (see Miteliell, 1970, for a review). According to Davenport ti al (1966), the dc\'elopment of" ibesc abnormalities depends on the iniaut's age; no stereotyped behaviour patterns were seen iu wild-born chimpanzees wliich were socially isolated for 6 months, beginning at the age of 18 months.in the course of our ehimpanzee breeding program, abnormal behaviour also developed under circumstances tliat are socially mueh better than total isolation. Nine chimpanzee iiifants, initially living v.'ith their mothers for different periods of time, all developed abnormalities when placed under human care in a nursery. This note describes the development o[ abnormalities following separation from ihe mother. Particular attention will be paid to the aetiologieal relationships between an abnormal pattern and its normal eoimterpart. Since the abnormalities observed are similar to those in human children, the results may cast light upon the origin of eom]>arable abnormal human behaviour patterns. M K'i'HODSThe infants were Fcparated Ironi their mother because of illness of either mother or infani, because of insufficient nursing by ihe mother or when they reached the age of 7 months, l'he ages at separation are given in Tal:)lc 1, Following separation, the babies were housed in a transparent incubator. Older apes spent most of their time with peers. During the daytime, the group used an cmirc rooni which was provided with objects for climbing; nights were spent together in a cage.One nurse (the second aiithor) cared for the younsr animals throughout the study period. She was assisted by two other nurses. Ape-nurse rommunicalion was reciprocal but restricted in time.Nursery data are based on diary notes ma

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