Four chimpanzee mother-infant pairs belonging to Tama Zoological Park were observed in order to see how this relationship develops. The main study run from August 1986 to December 1989. Each mother-infant pair was observed for 30 minutes once a week. All behavior patterns were recorded and analyzed.
The data showed that the process of the chimpanzee infant's development of attachment resembled closely that of humans from the pre-attachment-phase to a goal-corrected-partnership (Bowlby's model 1969). Moreover, three or four-year-old chimpanzee infants seemed to have some conflict with their mother, because ambivalent behavior occurred at that time. Infants whimpered for their mother without cause for fear and soon after the mother held them, they left her and whimpered again. Such ambivalent behavior patterns towards the mother are often observed in human infants.