ORIGINAL PAPER More than friends? Behavioural and genetic aspects of heterosexual associations in wild chacma baboons Elise Huchard & Alexandra Alvergne & Delphine Féjan & Leslie A. Knapp & Guy Cowlishaw & Michel Raymond Received: 27 June 2009 / Revised: 30 November 2009 / Accepted: 30 November 2009 / Published online: 23 December 2009 # Springer-Verlag 2009 Abstract In mammals, fathers are facultative caretakers, and male care is expected to evolve only if it is directed towards related young. Yet, in several promiscuous primate societies, males seem to care for infants despite a presumably low paternity confidence. In cercopithecines, cohesive asso- ciations (‘friendships’) between a lactating female and an adult male are frequent and provide the female and her infant with protection against various sources of aggression, including infanticide. However, the benefits gained by males through such relationships remain unclear, in part, because the relatedness between males and their protected infants has rarely been examined. Moreover, little is known about the nature of the cues underlying kin discrimination by males in societies where females mate polyandrously. In this study, we combine behavioural and genetic data from wild chacma baboons (Papio ursinus) in Namibia to investigate (1) whether males are related to their friend’ s infant and (2) whether similarity between the major histocompatibility complex (MHC) genotype of males and infants (potentially perceived through odour phenotype) favours the establish- ment of friendships. We first show that males share close genetic ties with their friend’ s infants, most often by having sired the infant. Secondly, we find that male–infant MHC (Class II–DRB) similarity, in contrast to paternity, does not predict male–infant associations. Overall, our results clarify the nature of the evolutionary benefits gained by males in these heterosexual associations, which can be considered as true paternal care. However, the proximate mechanisms underlying paternity recognition remain to be identified. Keywords Kin selection . Primates . Infanticide . Paternal investment . Papio ursinus . MHC Introduction Paternal care is traditionally defined as any behaviour that improves the survival chances of a given offspring at the cost of the father’ s ability to reproduce in the future (Trivers 1972). It is, therefore, expected to evolve only if the im- provement in offspring survival outweighs the potential Communicated by P. Kappeler Elise Huchard and Alexandra Alvergne contributed equally to this study. Electronic supplementary material The online version of this article (doi:10.1007/s00265-009-0894-3) contains supplementary material, which is available to authorized users. E. Huchard : A. Alvergne : D. Féjan : M. Raymond CNRS–Institut des Sciences de l’Evolution de Montpellier, Université Montpellier II, Montpellier, Hérault, France E. Huchard : G. Cowlishaw Institute of Zoology, Zoological Society of London, Regent’ s Park, London, UK L. A. Knapp Department of Biological Anthropology, University of Cambridge, Cambridge, UK Present Address: E. Huchard (*) Abteilung Verhaltensökologie und Soziobiologie, Deutsches Primatenzentrum, Kellnerweg 4, 37077 Göttingen, Germany e-mail: ehuchard@gmail.com Present Address: A. Alvergne Human Evolutionary Ecology Group, Department of Anthropology, University College London, 14 Taviton Street, London WC1H OBW, UK Behav Ecol Sociobiol (2010) 64:769–781 DOI 10.1007/s00265-009-0894-3