Infidelity and kin selection: does cheating seem as bad when it's "all in the family"?

The current study explored people's perceptions of how they would feel if their partners cheated on them by having sex with their relatives, such as if a man's wife had sex with his brother. Kin selection theory suggests that in such situations, victims of infidelity might feel slightly better if their partners had sex with biological relatives (compared to sex with nonrelatives) because some of the victims' genes could still get passed on through their relatives. In two experiments, participants reported how they would feel in various scenarios involving their partners having sex with participants' relatives and nonrelatives. As expected, participants generally reported being very disapproving of a partner's hypothetical infidelity with both their relatives and nonrelatives. However, contrary to predictions generated by kin selection theory, participants tended to report that they would feel worse if their partners had sex with their relatives. We propose several explanations for the current findings and discuss their implications for kin selection theory.