Alternative mating strategies, such as extra-group paternities (EGP), may be driven by the divergence of reproductive interests between males and females. EGPs may counteract negative fitness consequences, contribute to genetic variance or change group stability. They have broadly been described in several species of non-human primates, wherein genetic data of a few birth cohorts of a given social group revealed that a proportion of offspring are typically sired by males not resident to the social group at the time of offspring conception. Whereas much has been discussed about the occurrence of surreptitious matings, no work has been done to factors leading to EGPs. My study will comprise eight years of demographic, dominance and genetic data of all groups of the rhesus macaque population of Cayo Santiago. We will investigate EGPs from different perspectives including the group, male and female level.