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W9 Hill & Hurtado (2009)

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doi: 10.1098/rspb.2009.1061 , 3863-3870 first published online 19 August 2009 276 2009 Proc. R. Soc. B Kim Hill and A. Magdalena Hurtado gatherers - Cooperative breeding in South American hunter Supplementary data tml http://rspb.royalsocietypublishing.org/content/suppl/2009/08/18/rspb.2009.1061.DC1.h "Data Supplement" References http://rspb.royalsocietypublishing.org/content/276/1674/3863.full.html#related-urls Article cited in: http://rspb.royalsocietypublishing.org/content/276/1674/3863.full.html#ref-list-1 This article cites 40 articles, 7 of which can be accessed free Subject collections (2066 articles) behaviour Articles on similar topics can be found in the following collections Email alerting service here right-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. B To subscribe to This journal is © 2009 The Royal Society on June 11, 2011 rspb.royalsocietypublishing.org Downloaded from
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Cooperative breeding in South American hunter–gatherers Kim Hill * and A. Magdalena Hurtado School of Human Evolution and Social Change, Arizona State University, PO Box 872402, Tempe, AZ 85287-2402, USA Evolutionary researchers have recently suggested that pre-modern human societies habitually practised cooperative breeding and that this feature helps explain human prosocial tendencies. Despite circumstantial evidence that post-reproductive females and extra-pair males both provide resources required for successful reproduction by mated pairs, no study has yet provided details about the flow of food resources by different age and sex categories to breeders and offspring, nor documented the ratio of helpers to breeders. Here, we show in two hunter–gatherer societies of South America that each breeding pair with dependent offspring on average obtained help from approximately 1.3 non-reproductive adults. Young married males and unmarried males of all ages were the main food providers, accounting for 93–100% of all excess food production available to breeding pairs and their offspring. Thus, each breeding pair with dependants was provisioned on average by 0.8 adult male helpers. The data provide no support for the hypothesis that post-reproductive females are the main provisioners of younger reproductive-aged kin in hunter–gatherer societies. Demographic and food acquisition data show that most breeding pairs can expect food deficits owing to foraging luck, health disabilities and accumulating dependency ratio of offspring in middle age, and that extra-pair provisioning may be essential to the evolved human life history. Keywords: cooperative breeding; hunter–gatherers; life history 1. INTRODUCTION Evolutionary researchers have recently suggested that our species has been organized, throughout much of its natu- ral history, into partially kin-based resource acquisition and consumption units that engage in ‘cooperative breed- ing’ (e.g. Emlen 1995 ; Hrdy 1999 , 2005 , 2009 ; Kaplan et al . 2000 ; Wiessner 2002 ; Kaplan & Gurven 2005 ; Mace & Sear 2005 ). By cooperative breeding we mean
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