title: Men increase contributions to a public good when under sexual competition.
abstract: Why humans cooperate in large groups and with non-kin remains a puzzle for researchers across the natural and social sciences. Investigating whether cooperation is sexually selected could contribute to an understanding of the evolution of human cooperation. Competition for access to mates could indeed select for cooperation. Using controlled laboratory experiments, we analyse whether and how the sex composition of a social environment, testosterone level, and relationship status affect contributions to a public good. The results show that variation in sex composition alters the amount of money that single men (but not men in a couple or women) contribute to a public good. Notably, in line with the competitive helping hypothesis, awareness of the presence of a woman leads to larger contributions by single men, most likely by triggering their competitiveness to be the most cooperative man in the group. However, we find no link between basal testosterone level and cooperativeness. We argue that men, notably single men, adopt cooperative behaviours as a signalling strategy in the context of mate choice and hence that cooperation is partly sexually selected. Our findings highlight the need to consider sexual selection as an additional mechanism for cooperation.
authors.affiliation: Institute for Advanced Study in Toulouse, 21 allée de Brienne, 31015 Toulouse - France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Tognetti
authors.affiliation: CNRS, UMR 5474, LAMETA, av. R. Dugrand, C.S. 79606, 34960 Montpellier - France.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Dubois
authors.affiliation: Institute of Evolutionary Sciences, University of Montpellier, CNRS, IRD, EPHE, Montpellier - France.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Faurie
authors.affiliation: University of Montpellier &Institut Universitaire de France, LAMETA, av. R. Dugrand, C.S. 79606, 34960 Montpellier - France.
authors.forename: Marc
authors.initials: M
authors.lastname: Willinger
mesh_terms: D000328:Adult; D003163:Competitive Behavior / Q000502:physiology; D003299:Cooperative Behavior; D005260:Female; D005716:Game Theory; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D012737:Sex Factors; D012919:Social Behavior; D012931:Social Environment; D013739:Testosterone / Q000378:metabolism
chemical_list: D013739:Testosterone