Handedness and reproductive success in two large cohorts of French adults

Left- and right-handers in humans coexist at least since the Paleolithic, and this variation in hand preference has a heritable basis. Because there is extensive evidence of an association between left-handedness and several fitness costs, the persistence of the polymorphism requires an explanation. It is not known whether the frequency of left-handedness in Western societies is stable or not. If the polymorphism is at equilibrium and maintained by frequency dependence, it implies that the fitness of left-handers equals that of right-handers. On the contrary, if left- and right-handers have a different fitness, the polymorphism will evolve. Using two large cohorts of French adults (men and women), we investigated the relations between handedness and several estimators of the reproductive value: marital status, number of sexual partners (of the opposite sex), number of children, and number of grandchildren. Left-handers seem to have disadvantages for some life-history traits, such as marital status (for women) and number of children. For other traits, we observed sex-dependent interactions with socioeconomic status: for high-income categories, left-handed women report less sex partners and left-handed men have more grandchildren. These kinds of interactions are to be expected under the hypothesis that the polymorphism of handedness is stable.     

Testosterone Levels Are Negatively Associated with Childlessness in Males,but Positively Related to Offspring Count in Fathers

Variation in testosterone (T) is thought to affect the allocation of effort between reproductive and parenting strategies. Here, using a large sample of elderly American men (n = 754) and women (n = 669) we examined the relationship between T and self-reported parenthood, as well as the relationship between T and number of reported children. Results supported previous findings from the literature, showing that fathers had lower T levels than men who report no children. Furthermore, we found that among fathers T levels were positively associated with the number of children a man reports close to the end of his lifespan. Results were maintained when controlling for a number of relevant factors such as time of T sampling, participant age, educational attainment, BMI, marital status and reported number of sex partners. In contrast, T was not associated with either motherhood or the number of children women had, suggesting that, at least in this sample, T does not influence the allocation of effort between reproductive and parenting strategies among women. Findings from this study contribute to the growing body of literature suggesting that, among men, pair bonding and paternal care are associated with lower T levels, while searching and acquiring sex partners is associated with higher T levels.     

Marital Dissolution and Child Educational Outcomes in San Borja,Bolivia

Serial monogamy is likely an adaptive mating strategy for women when the expected future fitness gains with a different partner are greater than expected future fitness with one’s current partner. Using interview data from more than 400 women in San Borja, Bolivia, discrete-time event history analyses and random effects regression analyses were conducted to examine predictors of marital dissolution, separated by remarriage status, and child educational outcomes. Male income was found to be inversely associated with women’s risk of “divorce and remarriage,” whereas female income is positively associated with women’s risk of “divorce, but not remarriage.” Children of women who divorce and remarry tend to have significantly lower educational outcomes than children of married parents, but women with higher incomes are able to buffer their children from the negative educational outcomes of divorce and remarriage. Counter to predictions, there is no evidence that women with kin in the community have a significant difference in likelihood of divorce or a buffering effect of child outcomes. In conclusion, predictors of divorce differ depending on whether the woman goes on to remarry, suggesting that male income may be a better predictor of a serial monogamy strategy whereas female income predicts marital dissolution only. Thus, women who are relatively autonomous because of greater income may not benefit from remarriage.     

Partner Status Influences Women’s Interest in the Opposite Sex

Previous research has demonstrated that hormones, relationship goals, and social context influence interest in the opposite sex. It has not been previously reported, however, whether having a current sexual partner also influences interest in members of the opposite sex. To test this, we obtained explicit and implicit measures of interest by measuring men’s and women’s subjective ratings and response times while they evaluated photos of opposite-sex faces. Fifty-nine men and 56 women rated 510 photos of opposite-sex faces for realism, masculinity, attractiveness, or affect. We found that these subjective ratings were not influenced by partner status in either men or women. However, women who did not report having a current sexual partner spent more time evaluating the photos than women who did have partners, demonstrating greater interest in the photos. Sexual partner status did not predict men’s response times. These findings may reveal that relationship commitment in women suppresses interest in alternative partners.

Mate preferences and choices for facial and body hair in heterosexual women and homosexual men: influence of sex,population, homogamy,and imprinting-like effect

Recent research has reported that male body and facial hair influence women's mate preferences. However, it is not clear whether such preferences are typical for women or for individuals who prefer males as sexual partners. Here we explored body and facial hair in preferred and actual partners among men and women who prefer men as sexual partners. Including homosexual individuals provides a unique opportunity to investigate whether evolved mating psychologies are specific to the sex of the individual or sex of the partner. Based on an online survey of 1577 participants from Brazil and the Czech Republic, we found that, on average, homosexual men preferred hairier stimuli than heterosexual women, supporting past findings that homosexual men have strong preferences for masculine traits. Preferences for facial and body hair appear to be influenced less by sex of the preferred partner than sex of the individual, pointing to a possible sex-specific mating psychology. Further, Brazilians preferred bigger beards than Czechs, which was positively associated with the self-reported amount of beardedness in Brazil, suggesting that familiarity effects underpin cross-cultural differences in preferences for facial hair. Moreover, homosexual men preferred a self-similar degree of beardedness, and Czech women preferred a similar degree of beardedness as their fathers had during their childhood. However, these effects were not associated with the level of facial hair in their actual partners; in general, mate preferences and actual mate choices for facial and body hair differed. Thus, individual differences in some self-reported characteristics, cultural factors, and aspects of personal experience may modulate differences in preferences for masculine traits.     

Condition-dependent calibration of men’s uncommitted mating orientation: evidence from multiple samples

Physical strength and physical attractiveness are both hypothesized as indicators of overall phenotypic condition in humans. Strategic Pluralism Theory (Gangestad & Simpson, 2000) predicts that men’s orientation toward uncommitted mating is facultatively calibrated (i.e. contingently adjusted over ontogeny) in response to condition-dependent physical features, such as strength and attractiveness. Herein, we suggest that previous research bearing on this hypothesis has been limited because (a) researchers have often neglected to distinguish between mating orientations and past sexual behavior and (b) sample sizes have not always been large enough to reliably detect correlations of moderate magnitude. To address these issues and extend previous findings, we present aggregated data from three independent samples of young adults that permit us to examine multiple measures of physical strength and attractiveness in relation to uncommitted mating orientation, committed mating orientation, and past sexual behavior. As predicted, meta-analyses across samples demonstrated that strength and attractiveness were positively correlated with men’s (but not women’s) uncommitted mating orientation (but not committed mating orientation). In addition, strength (in men only) and attractiveness (in both sexes) positively predicted participants’ number of past sex partners. Moreover, path analyses demonstrated that the association of men’s physical features with their number of sex partners was mediated via uncommitted mating orientation. These results (a) provide the most extensive support to date for the hypothesis that men’s uncommitted mating orientation is calibrated to condition-dependent features and (b) clarify the sex-specific functional links among physical features, mating orientations and sexual behavior.     

Testosterone levels in women and men who are single, in long-distance relationships, or same-city relationships

Research points to an association between testosterone (T) and partnering in some women and men, and this association has been interpreted as an effect of either relationship status (i.e. differences in relationship status lead to differences in T) or relationship orientation (i.e. T is associated with the likelihood of entering relationships). To address whether physical partner presence was associated with decreased T, we examined T levels in people (72 women; 49 men) who were single, in long-distance relationships, or in same-city relationships. No participants were using exogenous hormones, including hormonal contraceptives. Participants provided a saliva sample and responded to questions about their relationship status. Single men had higher T than long-distance and same-city partnered men, which supports the relationship orientation interpretation. In contrast, same-city partnered women had lower T than single women and women in long-distance relationships, which supports the relationship status interpretation. We conclude that physical partner presence is not necessary to see an association between partnering and hormones in men (since same-city and long-distance partnered men had similar T levels), but may be necessary in women (since same-city partnered women had lower T than long-distance partnered women).     

Testosterone and partnering are linked via relationship status for women and ‘relationship orientation’ for men

Cross-cultural evidence links pair bonding and testosterone (T). We investigated what factors account for this link, how casual relationships are implicated, and whether gender/sex moderates these patterns in a North American sample. We gathered saliva samples for radioimmunoassay of T and self-report data on background, health, and social/relational variables from 115 women and 120 men to test our predictions, most of which were supported. Our results show that singles have higher T than long-term (LT) partnered individuals, and that casual relationships without serious romantic commitment are more like singlehood for men and LT relationships for women–in terms of T. We were also able to demonstrate what factors mediate the association between partnering and T: in women, frequency of partnered sexual activity mediated the effect in men, interest in more/new partners mediated the effect. This supported our prediction of relationship status interpretations in women, but relationship orientation in men. Results replicated past findings that neither sexual desire nor extrapair sexuality underlie the T-partnering link. We were able to rule out a large number of viable alternative explanations ranging from the lifestyle (e.g., sleep) to the social (e.g., social support). Our data thus demonstrate pattern and mediators for the development of T-pair bonding associations, and emphasize the importance of neither under- nor overstating the importance of gender/sex in research about the evolution of intimacy.     

Testosterone and partnering are linked via relationship status for women and ‘relationship orientation’ for men

Cross-cultural evidence links pair bonding and testosterone (T). We investigated what factors account for this link, how casual relationships are implicated, and whether gender/sex moderates these patterns in a North American sample. We gathered saliva samples for radioimmunoassay of T and self-report data on background, health, and social/relational variables from 115 women and 120 men to test our predictions, most of which were supported. Our results show that singles have higher T than long-term (LT) partnered individuals, and that casual relationships without serious romantic commitment are more like singlehood for men and LT relationships for women–in terms of T. We were also able to demonstrate what factors mediate the association between partnering and T: in women, frequency of partnered sexual activity mediated the effect in men, interest in more/new partners mediated the effect. This supported our prediction of relationship status interpretations in women, but relationship orientation in men. Results replicated past findings that neither sexual desire nor extrapair sexuality underlie the T-partnering link. We were able to rule out a large number of viable alternative explanations ranging from the lifestyle (e.g., sleep) to the social (e.g., social support). Our data thus demonstrate pattern and mediators for the development of T-pair bonding associations, and emphasize the importance of neither under- nor overstating the importance of gender/sex in research about the evolution of intimacy.     

Multiple partners are associated with higher testosterone in North American men and women

Previous research has shown that being partnered is associated with lower testosterone (T) in men and women. To address how multiple partners may be associated with T, we examined 47 men and 48 women who were single, monoamorously partnered (partnered), polyamorous (having multiple committed relationships), or in a polyamorous lifestyle but not currently multipartnered. Men who were partnered had lower T than all other men, and polyamorous men had higher T than single men. Polyamorous women had higher T than all other women. Measures of sociosexual orientation (SOI) and sexual desire differed in women by relationship type, but not in men. Findings are interpreted in light of 'competitive' and 'bond-maintenance' relationship orientations and statuses.     

If You’ve Got It,Flaunt It: Humans Flaunt Attractive Partners to Enhance Their Status and Desirability

Mating decisions are influenced by conspecifics’ mate choices in many species including humans. Recent research has shown that women are more attracted to men with attractive putative partners than those with less attractive partners. We integrate these findings with traditional accounts of social signaling and test five hypotheses derived from it. In our study, 64 men and 75 women were paired with attractive and unattractive opposite-sex putative partners and asked whether they would prefer to give surveys to peers or to older adults. Consistent with predictions, both men and women wanted to show off (flaunt) attractive partners by administering surveys to peers and both men and women wanted to hide (conceal) unattractive partners from peers by administering surveys to older adults. These decisions were mediated by how participants expected others to evaluate their status and desirability when they administered the surveys, consistent with partners serving a social signaling function in humans.     

Results of an explorative empirical study on human mating in Germany: handsome men, not high-status men, succeed in courtship

Recent research on human mating depicts men as searching for physical attractiveness (PA) and women as searching for status. To identify the mechanisms which lead to universal, biologically interpretable structures in social processes, we focused on the proximate causes for inter- and intrasexual differences in human mating preferences, attraction, and tactics. We collected data on 180 young singles (mean age 26.9 years) without a steady relationship. A questionnaire and a video sequence (20-30 seconds) of each subject was taken. Next, each video sequence was rated by approximately 20 individuals of the opposite sex, who also participated in this study. Surprisingly, the answers given by male and female subjects regarding sociosexual behaviour and mating preferences are predominantly congruent. Sex differences among preferences for good looking and high-status partners were small or even insignificant. Lower educated subjects had considerably higher status preferences than higher educated individuals. In both sexes, PA was much more preferred in a potential partner than status. For both sexes, physical appearance was decisive for the subject's dating attractiveness. Male, but not female dating attractiveness also correlates with a kind and charismatic appearance. Furthermore, there was a positive linear relationship between men's PA and their number of sexual partners within the last year. Men with more than four sexual partners were all above-average in PA, while the most attractive women had a medium number of sexual partners. However, in this respect, status had no influence. The results show that sex differences in mating are more complex than hitherto assumed.     

Dressed for sex: red as a female sexual signal in humans

Background

In many non-human primate species, a display of red by a female serves as a sexual signal to attract male conspecifics. Red is associated with sex and romance in humans, and women convey their sexual interest to men through a variety of verbal, postural, and behavioral means. In the present research, we investigate whether female red ornamentation in non-human primates has a human analog, whereby women use a behavioral display of red to signal their sexual interest to men.

Methodology/Principal Findings

Three studies tested the hypothesis that women use red clothing to communicate sexual interest to men in profile pictures on dating websites. In Study 1, women who imagined being interested in casual sex were more likely to display red (but not other colors) on their anticipated web profile picture. In Study 2, women who indicated interest in casual sex were more likely to prominently display red (but not other colors) on their actual web profile picture. In Study 3, women on a website dedicated to facilitating casual sexual relationships were more likely to prominently exhibit red (but not other colors) than women on a website dedicated to facilitating marital relationships.

Conclusions/Significance

These results establish a provocative parallel between women and non-human female primates in red signal coloration in the mating game. This research shows, for the first time, a functional use of color in women''s sexual self-presentation, and highlights the need to extend research on color beyond physics, physiology, and preference to psychological functioning.     

The dynamics of condom use with regular and casual partners: analysis of the 2006 national sexual behavior survey of Thailand

Objective

This study aims to determine factors associated with levels of condom use among heterosexual Thai males in sex with regular partners and in sex with casual partners.

Methods

The data used in this study are from the national probability sample of the 2006 National Sexual Behavior Study, the third nationally representative cross-sectional survey in Thailand. A subtotal of 2,281 men were analyzed in the study, including young (18–24) and older (25–59) adults who were residents of rural areas of Thailand, non-Bangkok urban areas, and Bangkok. Two outcomes of interest for this analysis are reported condom use in the past 12 months by males in relationships with the most recent regular and casual partners who were not sex workers. Chi-square statistics, bivariate regressions and the proportional odds regression models are used in the analysis.

Results

Condom use for men with their regular partner is revealed to be positively related to education, knowledge of condom effectiveness, and pro-condom strategy, and negatively related to non-professional employment, status of registered marriage, and short relationship duration. Condom use with casual partner is positively determined by education, condom knowledge, non-professional occupation, short relationship duration, and lack of history of paid sex.

Conclusion

The national survey emphasized the importance of risk perceptions and condom motivations variables in explaining condom use among men in Thailand. These factors include not only education and knowledge of condom effectiveness and pro-condom strategy but also types of partners and their relationship context and characteristics. Program intervention to promote condom use in Thailand in this new era of predominant casual sex rather than sex with sex workers has to take into account more dynamic partner-based strategies than in the past history of the epidemics in Thailand.     

Testosterone reactivity to facial display of emotions in men and women

Previous studies have examined testosterone's role in regulating the processing of facial displays of emotions (FDEs). However, the reciprocal process – the influence of FDEs, an evolutionarily ancient and potent class of social signals, on the secretion of testosterone – has not yet been studied. To address this gap, we examined the effects of emotional content and sex of facial stimuli in modulating endogenous testosterone fluctuations, as well as sex differences in the endocrine responses to faces. One hundred and sixty-four young healthy men and women were exposed, in a between-subjects design, to happy or angry same-sex or opposite-sex facial expressions. Results showed that in both men (n = 85) and women (n = 79), extended exposure to faces of the opposite sex, regardless of their apparent emotional content, was accompanied by an accumulation in salivary testosterone when compared to exposure to faces of the same sex. Furthermore, testosterone change in women exposed to angry expressions was greater than testosterone change in women exposed to happy expressions. These results add emotional facial stimuli to the collection of social signals that modulate endocrine status, and are discussed with regard to the evolutionary roles of testosterone.     

Sexual coercion and forced in-pair copulation as sperm competition tactics in humans

Rape of women by men might be generated either by a specialized rape adaptation or as a by-product of other psychological adaptations. Although increasing number of sexual partners is a proposed benefit of rape according to the “rape as an adaptation” and the “rape as a by-product” hypotheses, neither hypothesis addresses directly why some men rape their long-term partners, to whom they already have sexual access. In two studies we tested specific hypotheses derived from the general hypothesis that sexual coercion in the context of an intimate relationship may function as a sperm competition tactic. We hypothesized that men’s sexual coercion in the context of an intimate relationship is related positively to his partner’s perceived infidelities and that men’s sexual coercion is related positively to their mate retention behaviors (behaviors designed to prevent a partner’s infidelity). The results from Study 1 (self-reports from 246 men) and Study 2 (partner-reports from 276 women) supported the hypotheses. The Discussion section addresses limitations of this research and highlights future directions for research on sexual coercion in intimate relationships.     

Evidence for the influence of testosterone in the performance of spatial navigation in a virtual water maze in women but not in men

Testosterone (T) may be associated with enhanced spatial navigation in a number of rodent species, although the nature of the relation is equivocal. Similarly, numerous studies in humans generally have found that T is associated with enhanced spatial ability on a variety of paper and pencil tasks that may relate to navigational ability. However, relatively few studies have reported effects of T on navigational ability in humans. We investigated the relationship between endogenous T and performance on a virtual water maze (vWM) and mental rotations test (MROT). ELISA for T was performed on salivary samples that were obtained from participants before and after completion of both spatial tasks. Results indicated that women with low T required more time to locate the hidden platform in the vWM than either group of men or women with high T. Significant negative correlations were found for the entire sample between vWM performance and T, and between vWM latency to escape and MROT. Similar significant correlations were found in women but not men. Thus, our data support the position that T improves performance in the vWM in a linear fashion, most strongly in women. However, further work is needed to confirm this hypothesis in humans.     

Imagining the Western Husband: Thai Women's Desires for Matrimony,Status and Beauty

This article examines a group of Thai women's perceptions of western Caucasian men as ideal marriage partners and its impact on their sexual practices and relationship decisions. Based on conversations with women living in a ‘slum’ community in Bangkok, I argue that women who do not fit local ideals of light skin color, economic success and urban origins face obstacles among potential Thai suitors. Some of these women strategically prefer western suitors to local men. Through their relationship choices, these women upset local hierarchies of desire as they attempt to subvert skin color-bias and pose challenges to Thai marital traditions. At the same time, their relationship pursuits conform to gender expectations of the male breadwinner and female caretaker and may unintentionally reproduce skin color and status hierarchies. Although Thai women's sexual relationships with western men are not a new phenomena, they underscore the transnational nature of sexual desire and contemporary social change.     

Evidence of intralocus sexual conflict: physically and hormonally masculine individuals have more attractive brothers relative to sisters

Intralocus sexual conflict (IASC) occurs when sex-specific selection favors genes that increase fitness in one sex and decrease fitness in the other sex. The current study was designed to explore whether IASC occurs in humans. In a sample of siblings, we identified and measured sexually dimorphic traits and hormones within each sex that are related to fitness and are likely coded for by antagonistic genes: waist-to-hip ratio (WHR) and breast size in women, WHR and bicep size (an index of muscularity) in men, and estradiol (E) and testosterone (T) in both sexes. If these traits and hormones are coded for by genes under IASC, masculine or feminine expression of traits and hormones should differentially predict brothers' and sisters' fitness. Consistent with an IASC model, both men and women who were physically masculine for their sex reported higher mate value brothers relative to sisters. Similarly, in normal-weight individuals, E levels positively predicted the mate value of sisters relative to brothers and T levels positively predicted the mate value of brothers relative to sisters. We found no evidence that individuals with indicators of high genetic quality (i.e., physically masculine men and physically feminine women) share high mate value with all siblings, regardless of sibling sex. Results are novel and demonstrate for the first time that intralocus conflict in humans may influence the fitness of related individuals.     

Chlamydia trachomatis,Human Immunodeficiency Virus (HIV) Distribution and Sexual Behaviors across Gender and Age Group in an African Setting

ObjectiveThe purpose of this study was to (1) describe the distribution of Chlamydia trachomatis (CT) and Human Immunodeficiency Virus (HIV) cases across gender and age groups in Libreville (Gabon); (2) examine Gabonese Sexually Transmitted Infections (STIs)-related risk behaviour.MethodsThe sampled population was people attending the “Laboratoire National de Santé Plublique”. Between 2007 and 2011, 14 667 and 9 542 people respectively, were tested for CT and HIV infections. 1 854 of them were tested for both infections. We calculated CT and HIV rates across gender and age groups. Also analysed was the groups'' contribution to the general CT and HIV epidemiology.STIs-related risk behaviours were assessed in 224 men and 795 women (between July 2011 and March 2013) who agreed and answered a questionnaire including questions on their marital status, number of sex partners, sexual practices, history of STIs, sex frequency and condom use.ResultsData showed a 24% dropped in the CT infection rate between 2007 and 2010, followed by a 14% increase in 2011. The HIV infection rates for the same period were between 15% and 16%. The risk of a CT-positive subject getting HIV is about 0.71 times the risk of a CT-negative subject.Young adult aged between 18 and 35 years old represented 65.2% of people who had STIs. 80% of women and 66% of men confessed to an inconsistent use of condoms. 11.6% of women and 48% of men declared having multiple sex partners. 61% of questioned women and 67% of men declared knowing their HIV status.ConclusionsIn this Gabonese setting, the population-aged from18 to 35 years is the most affected by STIs. Other matters of concern are the inconsistent use of protection and sex with non-spousal or non-life partners.