Father-daughter inbreeding avoidance in a wild primate population Laura Muniz,1 Susan Perry,1,2 Joseph H. Manson,1,2 Hannah Gilkenson,1 Julie Gros-Louis,3 and Linda Vigilant1 1Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Germany, 2Department of Anthropology and Center for Behavior, Evolution and Culture, UCLA, 3Department of Psychology, Indiana University Abstract Inbreeding reduces fitness in various taxa, and several behavioral and physiological mechanisms have evolved that inhibit fertile matings between close kin. Most commonly, members of one or both sexes disperse before breeding. In primates, males usually disperse and females can benefit from long-term relationships with maternal kin within the group. Females thus risk breeding with their father if the tenure length of the dominant male, who usually sires most group offspring, exceeds the time it takes daughters to mature. Attempts to determine whether such co-resident father-daughter pairs systematically avoid inbreeding have produced equivocal results and no published studies have addressed this question by genetically ascertaining paternity in a wild population. We determined paternity for 117 wild white-faced capuchins (Cebus capucinus) born into our study population. As expected, the dominant alpha male in each group strongly monopolized reproduction. However, while siring 79% of the offspring born to unrelated females, alphas fathered only 6% (1 of 17) of the offspring conceived by their daughters during their tenures, providing evidence for effective inbreeding avoidance without female dispersal.