Prevalence studies indicate that about one in five women experience some degree of same-sex attraction. The evolutionary origins of such attraction are not well understood. Accordingly, this paper proposed a theoretical framework where, during the period of human evolution, same-sex attractions in women were under positive selection. The source of positive selection has been male preferences for opposite-sex sex partners who experienced same-sex attractions. This theoretical framework was used to generate four predictions that were tested in two online studies which employed a total of 1509 heterosexual participants. It was found that heterosexual women did not desire partners who experienced same-sex attractions, but a considerable proportion of heterosexual men desired partners who experienced same-sex attractions. In addition, it was found that men were more sexually excited than women by the same-sex infidelity of their partners, and they desired more than women, their opposite-sex partners to have sex with same-sex individuals. Finally, participants' preferences were contingent on the seriousness of the relationships, with same-sex attraction to be preferred more in short-term than in a long-term partner. These findings were employed in understanding the evolutionary origins of same-sex attraction in women.