It is well established that primates suffer and may survive illness and injury in the wild, but more equivocal is our understanding of how these affect reproductive fitness. This paper presents a functional and evolutionary framework for assessing nonhuman primate illness and injury by examining their timing in primate life history and their associations to subsistence, locomotion, and social behavior. The selective impact of illness and injury may take several forms, by affecting reproductive success through subadult mortality, mortality during reproductive years, restriction of a female's ability to care for her offspring, and impairment of male and female competition for mates.
Analysis may be made at the individual, local populational, or phylogenetic level. The available data indicate that there is considerable variability in the reproductive impact of illness and injury, and that the time of their occurrence in the life cycle is crucial. Broad distinctions in dietary strategies, locomotion, and social behaviors among primates are shown to be of limited use in interpreting evolutionary effects, and the observed variability in pathological profiles at the phylogenetic level suggests that smaller scale distinctions should be employed in future analyses. In addition, methodological inconsistencies seriously hamper these comparative studies.
With the steady increase in information on health and mortality patterns emerging from long-term field studies, integrated research efforts in ethology and osteology should permit us to go beyond this theoretical framework and demonstrate empirically the role of illness and injury in primate evolution.