The benefits of social capital: close social bonds among female baboons enhance offspring survivalINTRODUCTIONMATERIAL AND METHODSRESULTSDISCUSSIONResearch was reviewed and approved by the Animal Care and Use Committee at the University of Pennsylvania (Protocol no. 19001).We thank the Office of the President and the Department of Wildlife and National Parks of the Republic of Botswana for permission to conduct research in the Moremi Reserve. A. Mokopi, M. Mokopi, M. Heesen, C. Shaw, W. Smith and E. Wikberg provided valuable help with data collection and logistics in the field. J. Fischer, S. Johnson, D. Kitchen, R. Palombit and D. Rendall contributed to the demographic database and monitoring of female dominance rank. Field research was supported by grants to D.L.C and R.M.S. from the National Geographic Foundation, the Research Foundation of the University of Pennsylvania, the Institute for Research in Cognitive Science at the University of Pennsylvania and the National Institute of Health (HD-29433; MH62249); to J.B.S. from the National Science Foundation (9213586); to T.M.B. from the National Institutes of Health (NRSA fellowship F32 MH064232); and to R.M.W. from the German Science Foundation (WI 2637/2-1).REFERENCESdoi: 10.1098/rspb.2009.0681, 3099-3104 first published online 10 June 2009276 2009 Proc. R. Soc. B Moscovice, Roman M. Wittig, Robert M. Seyfarth and Dorothy L. CheneyJoan B. Silk, Jacinta C. Beehner, Thore J. Bergman, Catherine Crockford, Anne L. Engh, Liza R. female baboons enhance offspring survivalThe benefits of social capital: close social bonds among Referenceshttp://rspb.royalsocietypublishing.org/content/276/1670/3099.full.html#related-urls Article cited in: http://rspb.royalsocietypublishing.org/content/276/1670/3099.full.html#ref-list-1 This article cites 36 articles, 3 of which can be accessed freeSubject collections (1520 articles)evolution  (287 articles)cognition  (1129 articles)behaviour  Articles on similar topics can be found in the following collectionsEmail alerting service hereright-hand corner of the article or click Receive free email alerts when new articles cite this article - sign up in the box at the top http://rspb.royalsocietypublishing.org/subscriptions go to: Proc. R. Soc. BTo subscribe to This journal is © 2009 The Royal Society on March 18, 2010rspb.royalsocietypublishing.orgDownloaded fromThe benefits of social capital: close socialbonds among female baboons enhanceoffspring survivalJoan B. Silk1,*, Jacinta C. Beehner2,3, Thore J. Bergman2,4,Catherine Crockford5, Anne L. Engh6, Liza R. Moscovice7,Roman M. Wittig5, Robert M. Seyfarth6and Dorothy L. Cheney71Department of Anthropology, University of California, Los Angeles, CA 90095, USA2Department of Psychology,3Department of Anthropology, and4Department of Ecology andEvolutionary Biolog y, University of Michigan, Ann Arbor, MI 48109, USA5School of Psychology, University of St. Andrews, St. Andrews KY16 9JP, UK6Department of Biology, and7Department of Psychology, University of Pennsylvania,Philadelphia, PA 19104, USASociality has evolved in many animal taxa, but primates are unusual because they establish highly differ-entiated bonds with other group members. Such bonds are particularly pronounced among females inspecies like baboons, with female philopatry and male dispersal. These relationships seem to confer anumber of short-term benefits on females, and sociality enhances infant survival in some populations.However, the long-term consequences of social bonds among adult females have not been well estab-lished. Here we provide the first direct evidence that social relationships among female baboons conveyfitness benefits. In a group of free-ranging baboons, Papio cynocephalus ursinus, the offspring of femaleswho formed strong social bonds with other females lived significantly longer than the offspring of femaleswho for med weaker social bonds. These survival benefits were independent of m aternal dominance rankand number of kin and extended into offspring adulthood. In particular, females who formed strongerbonds with their mothers and adult daughters experienced higher offspring survival rates than femaleswho formed weaker bonds. For females lacking mothers or adult daughters, offspring survival was closelylinked to bonds between maternal sisters. These results parallel those from human studies, which showthat greater social integration is generally associated with reduced mortality and better physical andmental health, particularly for women.Keywords: social bonds; female relationships; baboons; primates; social capital; fitness1. INTRODUCTIONSociality has evolved in many animal taxa, but primates areunusual because they establish highly differentiated bondswith other members of their groups (Cheney & Seyfarth2007; Dunbar & Schultz 2007; Silk 2007). Femalebaboons (Papio cynocephalus spp.) form strong, equitableand enduring social bonds with particular females intheir group (Silk et al.1999; 2006a,b). Indirect evidencesuggests that these relationships may be adaptive. First,like other haplorhine primates, baboons have highly devel-oped social cognition, which allows them to track not justtheir own relationships but also those among other groupmembers (Cheney & Seyfarth 2007). Second, femalechacma baboons (P. c. ursinus)whoconcentratetheirgrooming on a small number of partners have lower gluco-corticoid levels and cope better with psychological stressorsthan females with more diffuse grooming networks(Crockford et al.2008; Wittig et al.2008). When a preferredpartner dies, glucocorticoid levels increase and femalesexpand their grooming networks in an apparent attempt toidentify new partners (Engh et al.2006). Here we providethe first direct evidence that social relationships amongadult females also have fitness consequences for individuals.Like other groups of cercopithecine primates, savannahbaboon groups are composed of a dominance hierarchy ofmatrilines and varying numbers of unrelated immigrantmales (Henzi & Barrett 2003; Swedell & Leigh 2006).Members of high-ranking matrilines enjoy a competitiveadvantage over members of lower-ranking ones, but themagnitude of the effect of dominance rank on femalereproductive success, as in most primate species, is gener-ally modest (Altmann & Alberts 2003; Cheney et al.2004).Although females interact with all other group members,they maintain close, long-term bonds with only a fewother females, who are usually close kin or