Social organisation and the distribution of relatedness in wild primate populations Nelly Ménard1 1Centre National de la Recherche Scientifique, Ethologie-Evolution-Ecologie, Station Biologique de Paimpont, Université de Rennes, France Abstract Social organisation is expected to shape the distribution of kinship within populations, a parameter that is relevant when studying kin selection and the level of cooperation. First, depending on the degree of philopatry, social groups will be made of kin related individuals or not. Second, according to the dominance profile that characterizes a species, the variance of the reproductive success of individuals, especially of males, will determine the distribution of paternally related individuals within and between groups. A large panel of social organisations leading to various distributions of kinship relationships has been described in primates. I will focus my talk on two species differing in their social organisation: a species with a multimale-multifemale structure whose females exhibit philopatry while males disperse around sexual maturity, and a species characterized by a one-male group structure and dispersal of both sexes. In the first species, female philopatry leads to the formation of matrilines that represent the smallest demographic unit within groups. The existence of such matrilines may have a decisive influence on the distribution of kin members within and between groups, in particular with regard to the issue of group fission processes. Within groups, reproductive success of males will depend on the relative effects of sexual promiscuity and strict dominance. In the second species, dispersal of both sexes should lead non-kin individuals to live together within groups, unless individuals disperse with kin. In addition, dominant males should monopolize reproduction within their harem, unless a non negligible part of offspring are the outcomes of sneaky matings. I will explore these questions in a comparison between macaques and gorillas. I will present results from long-term studies my colleagues, students and I have realized on wild populations of Barbary macaques and western lowland gorillas. In both cases, we collected behavioural and genetic data in order to investigate the relationship between group dynamics and patterns of relatedness.