Observations of physical abnormalities among the wild bonobos (Pan paniscus) of Wamba, Zaire

The wild bonobos (Pan paniscus) of Wamba, Zaire have an extremely high frequency of external abnormal traits. Out of 96 animals in a sample comprising all age and sex classes from two different natural groups, 46 individuals had at least one limb defect. The frequency of abnormalities was greater in males than in females, and increased directly with age. Almost all infants and juveniles had completely normal limbs, but virtually all males and over half the females which had reached their prime were found to have one or more limb defects. These findings indicate that congenital factors contribute little to the frequency of abnormalities in this sample. Survival rate is the same in individuals with defects as in those without defects. It appears that individual social status is far more important in procuring foods than locomotor ability. Thus, the operation of such abnormalities as a selective factor in intraspecific competition is minimized in the network of their social relations.