Male migration and inbreeding avoidance in wild rhesus monkeys

Genetic, demographic, and behavioral evidence from a population of wild rhesus monkeys (Macaca mulatta) were analyzed to test the widely held assumption that social subdivision of mammalian populations, as seen in the rhesus monkey, results in inbreeding. This assumption has been important in attempts to explain rapid rates of evolution among mammals. Demographic records were kept over a period of 42 months on a study population comprising 292 animals, subdivided into seven social groups. Blood was collected from about 80% of the animals in five of these groups. The ecology and behavior of one group was studied intensively. Groups were not found to be inbred. Rather, they were genetically similar and possessed an excess of heterozygotes at a number of loci, indicating high gene flow between groups and avoidance of consanguineous matings throughout the population. This is consonant with behavioral observations of male-limited natal group emigration, relatively short nonnatal group male tenure, and seemingly random distribution of male migration. These results, corroborated by genetic and behavioral data on other social mammals, raise questions about current theories that draw a direct causal link between social structure and inbreeding in mammals.