Why do men marry and why do they stray?

Department of Anthropology, University of New Mexico, Albuquerque, NM 87131, USA.
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.05). 08/2007; 274(1618):1643-9. DOI: 10.1098/rspb.2006.0437
Source: PubMed


Humans are quite unusual compared to other great apes in that reproduction typically takes place within long-term, iteroparous pairings--social arrangements that have been culturally reified as the institution of marriage. With respect to male behaviour, explanations of marriage fall into two major schools of thought. One holds that marriage facilitates a sexual division of labour and paternal investment, both important to the rearing of offspring that are born helpless and remain dependent for remarkably long periods (provisioning model). And the other suggests that the main benefits which men receive from entering into marriage derive from monopolizing access to women's fertility (mating effort model). In this paper, we explore extramarital sexual relationships and the conditions under which they occur as a means of testing predictions derived from these two models. Using data on men's extramarital sexual relationships among Tsimane forager-horticulturists in lowland Bolivia, we tested whether infidelity was more common when men had less of an opportunity to invest in their children or when they risked losing less fertility. We found that Tsimane men appear to be biasing the timing of their affairs to when they are younger and have fewer children, supporting the provisioning model.

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    • "Human mating systems include multiple types of relationships, from monogamous pair bonds to brief sexual affairs and extra-pair copulations (Gurven, Winking, Kaplan, von Rueden, & McAllister, 2009; Kelly, 1995; Pillsworth & Haselton, 2006; Winking, Kaplan, Gurven, & Rucas, 2007). This manifest variation, in turn, reflects a diverse range of mating orientations (Buss & Schmitt, 1993; Gangestad & Simpson, 2000). "
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    • "Consider: 1. Contemporary (marriage) value: Most modern marriage vows entail an explicit promise by the couple involved to be sexually exclusive to each other. Sexual fidelity is widely considered a virtue; adultery is considered a serious moral failure (see Winking et al. 2007), even a sin. Indeed, fully 97 % of respondents to one survey reported that married individuals should not have sex outside the relationship (Johnson et al. 2002). "
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    • "Previous data indicate a negative association between extramarital affairs and number of dependent offspring; thus, we expected to find that women suspecting husband infidelity in this dataset to be in their early twenties; yet, the average reported age was 29 with several accusers over 40. Contrarily, men of our previous study were more likely to have affairs when they were younger with fewer children to support [Winking et al., 2007a]. There are a few explanations for the difference in these male vs. female reported findings. "
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