In any event, it is also interesting to .note that in the study just described, the number of a woman's out-of-pair partners correlated with her "emotional attachment style." Each subject (male and female) was given an "attachment index," based on two different styles: "avoidant attachment" or "anxious attachment." Avoidant attachment included agreement or disagreement with such statements as "I am nervous whenever anyone gets too close to me,, while a typical sample item for the anxious-attachment scale would be "I often worry that my partner doesn't really love me." The results? Women with a higher level of anxious attachment had more out-of pair lovers, whereas those with a higher level of avoidant attachment had fewer. A woman's degree of physical symmetry did not predict her number of out-of-pair partners.
These combined findings are consistent with the basic biology of male-female differences: Men's out-of-pair sex correlated with a physical trait that presumably says something about their desirability, whereas women's out-of-pair sex correlated with a mental trait that presumably says something about their willingness to have such a relationship. The implication is that men are generally willing, that women are generally able, and that women are most sexual with men who are symmetrical.
Classically we believe that males care most about physical attractiveness, and males do, but males also can just have a lot of sex with a lot of different people so physical attractiveness actually matters less to males versus girls who are committed to pregnancy in which case physical attractiveness (which signals good traits) actually matters much much more and this is demonstrated in their behavior too. Guys are generally satisfied once they are in a relationship, whereas women continually seek better mates if they can (better = physical attractiveness...) ↩︎
—David P. Barash, The Myth of Monogamy, p. 77