An observation of a severely disabled infant chimpanzee in the wild and her interactions with her mother.

We report the physical and behavioral development of one severely disabled female infant chimpanzee (Pan troglodytes schweinfurthii) of the well-habituated M group in the Mahale Mountains National Park. We documented interactions between the infant and its mother and with other group members. Congenital disabilities occur in many primate species, including chimpanzees. However, there have been only a few case studies of congenitally disabled chimpanzee infants and no reports examining how a chimpanzee mother copes with such a disabled infant in the wild. The observed infant exhibited symptoms resembling Down syndrome, similar to those reported previously for a captive chimpanzee. The mother did not allow nonrelatives to take care of the infant even though she had been previously relatively tolerant of allomothering by nonrelatives. The mother's compensatory care for her infant's disabilities and allomothering of the infant by its sister might have helped it to survive for 23 months in the wild. Other group members did not show any aversive or fearful reactions to the disabled infant.