Changes in women's feelings about their romantic relationships across the ovulatory cycle

Abstract

According to the dual mating hypothesis, women possess two overlapping suites of mate-choice mechanisms: one leading to preferences for sexually desirable men who have high-fitness genes and one leading to preferences for men who are able to invest in a woman and her children. Evidence increasingly demonstrates that women's preference for sexual desirability (but not investment attractiveness) increases when women are most fertile within the ovulatory cycle. Little is known, however, about the implications of these preference shifts for women's relationships with their long-term partners. Using luteinizing hormone tests to verify ovulation, across two studies (Samples 1 and 2), we found that women whose partners were relatively low in sexual desirability felt less close to their partner (Samples 1 and 2) and were more critical of their partner's faults (Sample 2) on high-fertility days of the cycle just prior to ovulation compared with low-fertility days of the cycle. Women whose partners were relatively high in sexual desirability felt closer to their partner (Sample 1) and more satisfied with their relationship (Sample 2) on high- than low-fertility days of the cycle. There were no such shifts in women's commitment to their relationship. Therefore, partner sexual desirability predicts women's high-fertility assessments of relationship quality but not their intentions to stay in their relationship, consistent with the dual mating hypothesis. These findings suggest that variations across the ovulation cycle in women's reproductive hormones play an important role in relationship dynamics.

Introduction

A growing body of research indicates that women's mate preferences and attractions shift systematically across the ovulation cycle (reviewed by Gangestad and Thornhill, 2008, Haselton and Gildersleeve, 2011). This raises the question of whether there are corresponding changes across the cycle in women's feelings about their long-term romantic relationship. Virtually no prior work has investigated this question, despite romantic relationship feelings being central to the study of human behavior. We present evidence from two studies involving multiple assessments of women's relationship feelings and rigorous measures of cycle position. The studies show that women's feelings about their long-term relationship do change across the cycle. We report findings that suggest that variations across the cycle in women's reproductive hormones might play an important role in romantic relationship dynamics.

Many studies have demonstrated that women express stronger preferences for male characteristics that are hypothesized indicators of high-fitness genes on high- relative to low-fertility days of the cycle (reviewed in DeBruine et al., 2010, Thornhill and Gangestad, 2008). These characteristics include masculine faces (reviewed in DeBruine et al., 2010), masculine bodies (Gangestad et al., 2007, Little et al., 2007), and the natural body odors of men who have symmetrical faces and bodies (Gangestad and Thornhill, 1998, Rikowski and Grammer, 1999, Thornhill and Gangestad, 1999, Thornhill et al., 2003). These characteristics are associated with men's sexual attractiveness and men's desirability as short-term sex partners (Frederick and Haselton, 2007, Gangestad and Thornhill, 1997, Gangestad et al., 2007), and, indeed, increased preferences for sexually desirable characteristics at high-fertility are particularly pronounced—and sometimes only present—when women are considering men as short-term sex partners, rather than long-term relationship partners (Gangestad et al., 2004, Gangestad et al., 2007, Little et al., 2007, Penton-Voak et al., 1999). In contrast, women's preferences for characteristics that are desirable in a long-term romantic partner but are not strongly associated with sexual desirability, such as warmth, financial success, and faithfulness, either do not change across the cycle or are weaker on high- than low-fertility days of the cycle (Gangestad et al., 2007, Lukaszewski and Roney, 2009).

These preference shifts have been explained in terms of the dual mating hypothesis, which entails the notion that women's mate preferences serve two functions (Haselton and Gangestad, 2006, Pillsworth and Haselton, 2006b, Thornhill and Gangestad, 2008). First, women's choices of long-term relationship partners influenced the material and social resources available to their children. All else being equal, an ancestral woman who formed a relationship with a man who invested highly in her and her children probably had children who were more likely to survive than the children of a woman who had a less investing partner (Buss, 1994, Pillsworth and Haselton, 2006b). Therefore, it is plausible that women possess evolved preferences for long-term relationship partners who are high in investment attractiveness (possessing characteristics that indicate they are able to invest highly in a woman and her children).

Second, ancestral women's choices of sex partners influenced the genes her future children could inherit. All else being equal, a woman who conceived children with men who possessed high fitness genes (e.g., relatively free of deleterious genetic mutations) probably had children who were more likely to survive and later reproduce than the children of a woman who chose a less genetically fit partner (Gangestad and Simpson, 2000). Therefore, it is also plausible that women possess adaptive preferences for sex partners who are high in sexual desirability (possessing characteristics that indicate they have high-fitness genes they can pass on to offspring). Sexually desirable characteristics such as symmetry and masculinity are hypothesized to have been indicators of high-fitness genes in men in ancestral environments (Gangestad and Simpson, 2000). For example, a recent meta-analyses found that men's symmetry was a small but robust predictor of a number of fitness-relevant outcomes, such as health and sex partner number (Van Dongen and Gangestad, 2011).

Because women can only secure genetic benefits for offspring when fertile, the logic of the dual mating hypothesis leads to the prediction that women's preference for sexually desirable characteristics that ancestrally indicated high-fitness genes will be greatest within the fertile window of the ovulatory cycle (Pillsworth and Haselton, 2006b, Thornhill and Gangestad, 2008). In contrast, because women could secure material and social benefits for offspring throughout the cycle, the dual mating hypothesis leads to no expectation that women's preference for characteristics contributing to a man's investment attractiveness will shift across the cycle. These predictions have been supported by a number of studies (reviewed in DeBruine et al., 2010, Thornhill and Gangestad, 2008).

The dual mating hypothesis has implications for women's long-term romantic relationships. An ancestral woman who partnered with a man who was high in sexual desirability and investment attractiveness could have gained both genetic and investment benefits from a single long-term relationship. In contrast, an ancestral woman partnered with a man who was high in investment attractiveness but low in sexual desirability could have enhanced her reproductive success through engaging in surreptitious sexual affairs with men other than her primary partner on high-fertility days of the cycle (Gangestad and Simpson, 2000, Pillsworth and Haselton, 2006b, Thornhill and Gangestad, 2008). Consistent with this logic, women in relationships with men who lack characteristics hypothesized to indicate high-fitness genes report feeling more attracted to men other than their primary partner on high-relative to low-fertility days of the cycle (reviewed in Larson, et al., 2012; also see Puts et al., 2012a, Puts et al., 2012b, Thornhill et al., 1995 for related evidence).

Whether these fertility-based changes in preferences and desires across the cycle affect women's long-term romantic relationships remains unknown. Based on the research described above, one might expect that women's feelings about their relationship will also change across the cycle, such that women partnered with men who are relatively low in sexual desirability will feel more negatively about their relationship at high relative to low fertility.

Only one prior study examined changes in women's relationship feelings across the cycle. Jones and colleagues asked 93 naturally cycling women how happy and committed they were in their romantic relationship and estimated each woman's progesterone and estrogen levels based on women's recalled last menstrual onset (Jones et al., 2005). They did not observe a significant association between relationship happiness and estimated hormone levels, but found a positive association between relationship commitment and estimated progesterone levels, suggesting that women's commitment to their relationship might change across the cycle. However, the study used a forward-counting method relying on a women's recalled last menstrual onset, which can be imprecise (Chiazze et al., 1968, Fehring et al., 2006, Waller et al., 2000). The study also did not examine whether the women in the study had partners who possessed the characteristics women find especially attractive at high fertility. This important factor is likely to moderate changes in women's relationship feelings across the cycle. Given these issues, how women's relationship feelings change across the cycle and for which women these changes are most pronounced remain open questions.

In a set of two similar studies (presented as Sample 1 and Sample 2), we examined how women's feelings about their relationship changed across the ovulation cycle and whether these changes depended on women's ratings of their partner's sexual desirability. Women rated their relationship along various dimensions at high and low fertility. This within-woman design eliminates noise created by between-women variation, therefore providing a sensitive test of changes across the cycle. Hormone tests confirmed that all women in the sample ovulated near their high-fertility session, indicating that all putatively high-fertility sessions were, in fact, scheduled on high-fertility days of the cycle. Details on participant characteristics and scheduling presented separately for each sample can be found in the supplemental materials.