The predictability of genetic structure from social structure and differential mating success was tested in wild baboons. Baboon populations are subdivided into cohesive social groups that include multiple adults of both sexes. As in many mammals, males are the dispersing sex. Social structure and behavior successfully predicted molecular genetic measures of relatedness and variance in reproductive success. In the first quantitative test of the priority-of-access model among wild primates, the reproductive priority of dominant males was confirmed by molecular genetic analysis. However, the resultant high short-term variance in reproductive success did not translate into equally high long-term variance because male dominance status was unstable. An important consequence of high but unstable short-term variance is that age cohorts will tend to be paternal sibships and social groups will be genetically substructured by age.In this study, we combined molecular genetic data with long-term behavioral and demographic data to examine several aspects of behavior-genetic relationships that are central to the evolution of primate social systems. The first of these is the priority-of-access model, which predicts that dominance status among adult males determines access to estrous females (1) and that variability in the number of offspring fathered by males will, therefore, directly reflect both the males' dominance status and the number of simultaneously estrus females (2). Second, we investigated the widespread assumption that short-term differences in mating success or paternity success are stable and, therefore, predictive of lifetime differences in reproductive success (for review, see refs. 3 and 4). Third, we examined the hypothesis that a species' dispersal system and social structure produce predictable population substructure within groups (5, 6). For example, adult males within groups of baboons and many other cercopithecine primates are predicted to be less closely related than are adult females, and relatedness should be greater within than between matrilines.The study was conducted on a group of individually known wild savannah baboons, Papio cynocephalus, in Amboseli, Kenya (7). Like most cercopithecine primates and many other mammals (5,(8)(9)(10)(11)