Extra-pair sex

And this is not about having an extra pair of socks ... although those can always come in handy:

"Extra-pair sex (i.e., sex outside a current, ongoing relationship) is one form of short-term, opportunistic mating. If women evolved to desire men with greater heritable fitness (independent of the investment and resources that men provided), more symmetrical men should have more extra-pair partners (see Benshoof & Thornhill, 1979; Smith, 1984). Gangestad and Thornhill (1997b) found that men’s FA does predict their number of extra-pair sex partners, r = -.17 (reflecting a latent correlation between extra-pair partners and developmental imprecision of about -.36; Gangestad & Thornhill, in press). Once potential artifacts were controlled (e.g., social status, SES in family of origin, anticipated future salary), the correlation between FA and extra-pair sex increased slightly. Neither men's social status nor their resources (as indexed by their SES and their anticipated future salary) predicted their frequency of extra-pair sex. Although Perusse (1993) has found that men with higher status report having more sex partners than men with lower status, this effect did not hold for married men in his sample. Thus, it is unclear whether men with higher status (e.g., wealthier men) have more extra-pair mates than men with lower status."