Abstract
Despite the importance of extrapair copulation (EPC) in human evolution, almost nothing is known about the design features of EPC detection mechanisms. We tested for sex differences in EPC inference-making mechanisms in a sample of 203 young couples. Men made more accurate inferences (φmen = 0.66, φwomen = 0.46), and the ratio of positive errors to negative errors was higher for men than for women (1.22 vs. 0.18). Since some may have been reluctant to admit EPC behavior, we modeled how underreporting could have influenced these results. These analyses indicated that it would take highly sex-differentiated levels of underreporting by subjects with trusting partners for there to be no real sex difference. Further analyses indicated that men may be less willing to harbor unresolved suspicions about their partners’ EPC behavior, which may explain the sex difference in accuracy. Finally, we estimated that women underreported their own EPC behavior (10%) more than men (0%).
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Notes
In principle, we could also treat the inference (rather than the certainty associated with it) as a continuous variable. However, this leads to unnatural coding of the correctness of inferences. Suppose, for instance, that person A thought there was an 80% chance that her partner had had an affair, whereas person B reported a 90% chance that her partner had had an affair. Assume also that the partners of both of these people admitted to having EPCs. Under this coding scheme, we would say that A is 80% correct, B is 90% correct, and B is 10% more correct than A. However, we don’t believe that people think this way. A and B would probably say that they are both inferring that their partners had affairs, and that both were correct. But they would probably agree that B was more certain about her inference than A.
It is possible that some subjects who answered “yes” to the “to your knowledge” question were not actually 100% certain that their partners had affairs. However, it seems reasonable to assume that if there were such subjects, they would still have been at least 50% certain that their partner had an affair. Thus, this would not influence our coding of them as being suspicious that their partner had an affair or the results of our analyses about accuracy and error bias that we report. It would only influence the certainty of that inference, and the results that depend on certainty.
Of course, subjects might have had a different view of whether their own extrapair sexual behavior was illicit, but they were only asked to provide information on the affair behavior of their partners, not themselves.
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Acknowledgments
PWA was supported by a National Research Service Award from the National Institutes of Health, P32 MH-20030 (PI: Michael C. Neale). Rosalind Arden, Judith Easton, Todd Shackelford, Andy Thomson, Tina Wagers, and two anonymous reviews provided comments. Chuck Gardner provided statistical advice.
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Andrews, P.W., Gangestad, S.W., Miller, G.F. et al. Sex Differences in Detecting Sexual Infidelity. Hum Nat 19, 347–373 (2008). https://doi.org/10.1007/s12110-008-9051-3
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DOI: https://doi.org/10.1007/s12110-008-9051-3