The relation between testosterone and aggression has been relatively well documented in men, but it is less well understood in women. Here we assessed the relationship between salivary testosterone and reactive aggression (i.e., rejection rate for unfair offers) in the Ultimatum Game. Forty naturally cycling women were tested twice, once in the late follicular phase (around ovulation) and once during the luteal phase. Ovulation was determined using urine test strips measuring luteinizing hormone levels. Salivary samples were assayed for testosterone, estradiol, progesterone, and cortisol at both test sessions. There was no association with the cycle, but multilevel modeling revealed a significant within-participant association between testosterone and rejection rate for extremely unfair offers (i.e., high reactive aggression), indicating that women showed greater reactive aggression when their testosterone levels were higher. Additionally, we found that women with relatively high individual concentrations of testosterone were more likely to reject extremely unfair offers than women with relatively low concentrations of testosterone. This study is the first to demonstrate that women react more aggressively in response to provocation when their testosterone level is high than when their testosterone is low, suggesting that testosterone plays an important role in the regulation of women's aggressive behavior following social provocation.

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Havlíček et al. (2015) have provided an excellent critique of the current status of the "ovulatory shift" hypothesis of women's sexual attractiveness, and the "human estrus" hypothesis of female mate choice. The first of these hypotheses posits that women become significantly more sexually attractive (e.g., due to changes in visual or vocal traits) during the periovulatory phase of the menstrual cycle. The second hypothesis proposes that women are significantly more attracted to certain masculine traits (e.g., masculinized faces) during the fertile phase of the cycle and that female mate choices are significantly affected on this basis. Yet, as Havlíček et al. point out, "physical changes in women's appearance around ovulation are almost beyond our capacity to measure." Likewise, "even detailed acoustic analysis precludes unequivocal identification of the follicular phase." Such facts confirm that men are unable to determine when women are likely to ovulate, and that "shifts" in attractiveness around ovulation are biologically trivial, if they exist at all. As for increased responsiveness to masculine traits during the fertile phase of the cycle, these are likewise very small, if they exist at all (e.g., see Peters et al. 2009; Harris 2011, 2013), and probably have no relevance to human sexual behavior in the real world (Dixson 2009, 2012). Havlíček et al. rightly emphasize that hormones influence human sexual attractiveness via effects that are expressed over the long term, rather than during individual menstrual cycles. Thus, women who have consistently higher levels of estradiol have more attractive faces (Law Smith et al. 2006). Women who have a healthy distribution of body fat, and an "hourglass" body shape, have higher circulating levels of estrogen and are more fertile (Jasieñska et al. 2004; Singh et al. 2010). The reason why cues relating to underlying reproductive health and fertility do not fluctuate significantly during menstrual cycles, relates to the long-term nature of reproductive processes and mate-choice decisions that have characterized the course of human evolution. Long-term monogamous or polygynous relationships between women and men occur in the majority of recent human cultures around the world, and would likely have been present in our African ancestors (Dixson 2009). We reproduce slowly, and human offspring are dependent on their parents for many years. Where masculine mate choices are concerned, cues that advertise long-term female health and fertility are thus adaptive; likewise, female mate choice is focused on long-term reproductive outcomes, rather than on periovulatory, extrapair copulations in quest of "better genes." Perhaps, as Havlíček et al. suggest, women who exhibit generally higher levels of circulating estradiol might also show some greater propensity to display small changes in attractiveness (and behavior) during the menstrual cycle. These small changes, if they exist, would constitute side effects, and epiphenomena, rather than being reproductive adaptations. In which c...

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