Impact of relational proximity on distress from infidelity

From the book : Evolutionary Psychology 7 issue 4 : 560-580.
Men are generally more distressed by a partner’s sexual infidelity whereas women are generally more distressed by a partner’s emotional infidelity.
The importance of the identity of the interloper, however, has been neglected.
We explored the influence of relational proximity (i.e., the degree of genetic relatedness) on distress about infidelity.
In Study 1, participants were most distressed when the imagined infidelity occurred between their current mate and close kin.
In Study 2, relational proximity mattered more than the type of sexual behavior, the likelihood of contracting a sexually transmitted disease, and the likelihood of the infidelity leading to a damaged reputation.
Together, the results indicate that identity matters, especially if the interloper is someone with whom we have familial bonds.