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Speakers modulate their voice when talking to infants, but we know little about subtle variation in acoustic parameters during speech in adult social interactions. Because tests of perception of such variation are hampered by listeners' understanding of semantic content, studies often confine speech to enunciation of standard sentences, restricting ecological validity. Furthermore, apparent paralinguistic modulation in one language may be underpinned by specific parameters of that language. Here we circumvent these problems by recording speech directed to attractive or unattractive potential partners or competitors, and testing responses to these recordings by naive listeners, across both a Germanic (English) and a Slavic (Czech) language. Analysis of acoustic parameters indicates that men's voices varied F 0 most in speech towards potential attractive versus unattractive mates, while modulation of women's F 0 variability was more sensitive to competitors, with higher variability when those competitors were relatively attractive. There was striking similarity in patterns of social context-dependent F 0 variation across the two model languages, with both men's and women's voices varying most when responding to attractive individuals. Men's minimum pitch was lower when responding to attractive than unattractive women. For vocal modulation to be effective, however, it must be sufficiently detectable to promote proceptivity towards the speaker. We showed that speech directed towards attractive individuals was preferred by naive listeners of either language over speech by the same speaker to unattractive individuals, even when voices were stripped of several acoustic properties by low-pass filtering, which renders speech unintelligible. Our results suggest that modulating F 0 may be a critical parameter in human courtship, independently of semantic content.

Hormonal variation over the menstrual cycle alters women's preferences for phenotypic indicators of men's genetic or parental quality. Hormonal contraceptives suppress these shifts, inducing different mate preference patterns among users and non-users. This raises the possibility that women using oral contraception (OC) choose different partners than they would do otherwise but, to date, we know neither whether these laboratory-measured effects are sufficient to exert real-world consequences, nor what these consequences would be. Here, we test for differences in relationship quality and survival between women who were using or not using OC when they chose the partner who fathered their first child. Women who used OC scored lower on measures of sexual satisfaction and partner attraction, experienced increasing sexual dissatisfaction during the relationship, and were more likely to be the one to initiate an eventual separation if it occurred. However, the same women were more satisfied with their partner's paternal provision, and thus had longer relationships and were less likely to separate. These effects are congruent with evolutionary predictions based on cyclical preference shifts. Our results demonstrate that widespread use of hormonal contraception may contribute to relationship outcome, with implications for human reproductive behaviour, family cohesion and quality of life.

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Numerous recent studies document peri-ovulatory increases in women's physical attractiveness and in their preferences for certain male traits, which appear to be linked to cyclical fluctuation in levels of ovarian hormones. Changes in physical traits are subtle, leading to the widespread conclusion that cues of ovulation are adaptively concealed. It has been argued that concealment enables women to pursue a mixed-mating strategy characterized by pair-bonding with opportunistic extra-pair copulation with high quality mates when conception is possible. Men's preferences for peri-ovulatory cues and women's cyclical preference shifts are thus also argued to reflect distinct psychological adaptations. Here, we re-interpret the evidence for each of these putative adaptations and argue that cyclic changes need not result from incomplete concealment of ovulatory status. We also emphasize that ovarian hormone levels underpin between-individual differences in both women's attractiveness and their mate preferences, which influence the sexes' mate choice decisions. We contrast the salience and efficiency of these within-and between-individual effects, and suggest that, while both effects have the potential to influence mating behavior, the between-individual effects are stronger and more robust. This introduces the possibility that both men's increased attraction towards peri-ovulatory women and women's cyclical shifts in preference for certain male traits may not constitute adaptations per se, but are, instead, inevitable byproducts, or 'perceptual spandrels', of putative adaptations related to between-individual differences in reproductive potential. Our framework parsimoniously explains several observable phenomena, and potentially could transform the way evolutionary researchers interpret changes in behavior associated with the menstrual cycle.

Despite frequent sanctions and potentially serious consequences, extra-dyadic involvements are a relatively common phenomenon. Previously, potential links among extra-dyadic involvements and personal or interpersonal characteristics were extensively explored. However, the developmental aspects of extra-dyadic relationships have been rather overlooked to date. Here, we focus on the association between self-reported extra-dyadic tendencies and behavior, and previous experience with extra-dyadic sex in prior romantic relationships and in the primary family. We asked both members of 86 long-term cohabiting couples to complete several inventories assessing various aspects of the relationship satisfaction, sociosexuality and extra-dyadic intentions and behavior. As in previous studies, we found a lower level of overall Dyadic Adjustment and in the subscales Affectional Expression and Dyadic Consensus, in particular, among women but not men who reported extra-pair sex. Neither experience with own nor partners' infidelity in previous relationships was linked to reported extra-pair sex in the current relationship. However, men who reported their fathers but not mothers being unfaithful were also significantly more often unfaithful and showed a higher level of extra-dyadic intentions. There was no association between parental infidelity and extra-pair sex or extra-dyadic intentions in women. Our results suggest that experience of infidelity within the primary family has an impact on subsequent behavior. However, this is the case only in men. Women's extra-dyadic activities seem to be affected instead by the quality of the current relationship. Future research is needed to test the influence of ontogenetic and hereditary factors on the development of infidelity tendencies.

Hormonal fluctuation across the menstrual cycle explains temporal variation in women's judgment of the attractiveness of members of the opposite sex. Use of hormonal contraceptives could therefore influence both initial partner choice and, if contraceptive use subsequently changes, intrapair dynamics. Associations between hormonal contraceptive use and relationship satisfaction may thus be best understood by considering whether current use is congruent with use when relationships formed, rather than by considering current use alone. In the study reported here, we tested this congruency hypothesis in a survey of 365 couples. Controlling for potential confounds (including relationship duration, age, parenthood, and income), we found that congruency in current and previous hormonal contraceptive use, but not current use alone, predicted women's sexual satisfaction with their partners. Congruency was not associated with women's nonsexual satisfaction or with the satisfaction of their male partners. Our results provide empirical support for the congruency hypothesis and suggest that women's sexual satisfaction is influenced by changes in partner preference associated with change in hormonal contraceptive use.

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