Source: Gurit Birnbaum

A high-quality offers many benefits, including better health and higher reproductive fitness. In their attempt to form such a beneficial relationship, people are guided by mechanisms that evolved to help them identify the most suitable person in their social milieu.

For example, they show a preference for body odor that signals compatibility with potential mates' immune system.1 When they find such a desirable partner, people typically strive to maintain the relationship by employing strategies that protect it against the allure of alternative mates (e. ., being less attentive to and devaluing the of alternatives).2

Commonly used contraceptive pills may change natural mate preferences however. These pills introduce hormones that suppress ovulation and lead to temporary fertility loss, similarly to what happens during . Consequently, heterosexual women's perception of men may serve a different function than that occurring around ovulation: They may pursue a cooperative partner who assists with child care rather than a genetically compatible partner.3 Women may therefore revert to having opposite mate preferences, becoming fixed on seeking less genetically compatible men whose body odor resembles that of their apparently supportive genetic relatives.4

To the extent that contraceptive pill use alters mate preferences, women who had taken contraceptives while meeting their partner and later discontinued their usage (as many do when they wish to conceive) may feel disenchanted with their initial partner choice. Indeed, the use of hormonal contraceptives may not only affect initial partner choice but also have unintended consequences for women’s relationship satisfaction if contraceptive pill use subsequently changes. Prior studies have provided evidence for this hypothesis, indicating that women who had used hormonal contraceptives when they first met their partner and then ceased to take them experience lower levels of sexual and relationship satisfaction5 and are more likely to get .6

In research7 published recently in Evolutionary Psychological Science, my colleagues and I sought to examine whether the adverse relationship implications of cessation of contraceptive pill use in women who used pills during relationship onset extend to an increased likelihood of to alternate partners. In two studies, we examined whether women who had used hormonal contraceptives during relationship formation and later discontinued their usage would be particularly likely to find attractive alternative mates sexually appealing during the fertile phase of the menstrual cycle, as compared to women who either had not used pills at relationship formation or had done so but did not stop using the pills.

In Study 1, we examined whether heterosexual women who had used pills while meeting their current partner but had discontinued their usage would be particularly likely to experience sexual desire for attractive alternate mates. For this purpose, romantically involved female participants watched videos of two men who introduced themselves as potential partners on dating sites. One of these men was conventionally sexually attractive and described himself as a "bad boy," using traits that are associated with masculinity but low dependability (e.g., , easily bored, adventurous). The other man was average-looking and described himself as an "ordinary guy." After watching each video, participants described in narrative form an imaginary date with the man in the video. These descriptions were coded for written expressions of sexual desire for each man. The expressions of desire included expressed interest in presexual or sexual activity, such as kissing, making out, and having sexual intercourse, as well as descriptions of actual engagement in presexual and sexual interactions.

The findings revealed that the women who were currently in high-fertility phase and had used pills while meeting their current partner but had discontinued their usage were more likely to experience sexual desire for the attractive "bad boy" than for the average-looking "ordinary guy," However, the "bad boy" and the "ordinary guy" differed not only in physical attractiveness but also in dependability. Hence, it is unclear whether women preferred the "bad boy" because of his attractiveness or his undependability.

To address this limitation, in Study 2, we included no information about the men's characteristics other than their appearance, so that the women were exposed to men who differed from each other mainly in their physical attractiveness. Specifically, romantically involved female participants performed a visual cueing computerized task that assessed how efficient they were at withdrawing their from photos of attractive and average-looking men in order to categorize an object appearing in a different location on the screen. This task involved less conscious, rationally based preferences than the measures employed in previous studies. Hence, it was less likely to evoke demand characteristics (or other motivational biases) when recording participants' reactions to alternative mates.

Study 2 replicated Study 1's findings, showing that the women who were currently in high-fertility phase and had used pills while meeting their current partner but discontinued their usage were especially likely to monitor attractive alternative mates. Together, these studies demonstrated that women who had stopped using pills and were currently in high-fertility phase were particularly vulnerable to feeling desire for attractive alternatives, suggesting that the disillusionment that follows the cessation of pill use lessens women's to employ strategies that protect their relationship from attractive alternatives.

These conclusions, however, should be viewed with caution. For one, the validity of the counting methods used in this research to estimate the fertile window is modest. In addition, although we assessed approach tendencies toward possible mates, the participants in our research did not actually encounter those men. Hence, it is unclear whether they would have acted on their expressed desires and actually flirted with alternative mates. Finally, in spite of collectively showing a consistent results pattern, our studies are individually underpowered due to small sample size.

Notwithstanding these limitations, our research is the first to indicate that discontinuing hormonal contraceptives may push women, at least those who had used contraceptive pills during relationship formation, closer to becoming involved in an extradyadic affair.

This post also appeared here.

Here's my TEDx talk on why humans make so complicated.