اثرات هورمونی در اولویت های مردانگی صورت زنان: تاثیر بارداری، بعد از زایمان و استفاده از پیشگیری از بارداری هورمونی
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|38055||2015||6 صفحه PDF||سفارش دهید||5440 کلمه|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Biological Psychology, Volume 104, January 2015, Pages 35–40
Abstract Here, we investigate changes in women's facial masculinity preferences across pregnancy and the post-partum period. The majority of previous research demonstrating changes in women's masculinity preferences has examined the impact of hormonal variation across the female menstrual cycle. Hormonal changes experienced during pregnancy and the post-partum period, critical periods in women's reproductive life histories, are considerably more extreme than the variation that occurs across the menstrual cycle, suggesting that differences in preferences may also be displayed during these times. We find that women's preference for masculinity in men's faces, but not women's faces, decreases in the post-partum period relative to pregnancy. Furthermore, when compared to a sample of nulliparous control participants, post-partum participants showed different masculinity preferences compared with women who were using hormonal contraception, with the direction of this difference dependent upon the sex of the face assessed.
1. Introduction A large number of studies indicate that women's preference for masculinity in male faces is moderated by their menstrual cycle stage. For example, in the late follicular phase of the cycle, when oestrogen levels are relatively high and conception risk is highest, women have stronger preferences for facial masculinity than they do in the luteal phase of the cycle when oestrogen and conception risk are low (Little et al., 2008, Little and Jones, 2012, Penton-Voak and Perrett, 2000 and Penton-Voak et al., 1999). Increased attraction to masculinity during the late follicular phase has likewise been documented in women's ratings of male voices (Feinberg et al., 2006 and Puts, 2005), bodies (Little, Jones, & Burriss, 2007), and masculine characteristics in point-light displays of biological motion (Provost, Troje, & Quinsey, 2008, but see also Peters, Simmons, & Rhodes, 2009). An increased preference for related traits, such as dominant behavioural displays (Gangestad, Simpson, Cousins, Garver-Apgar, & Christensen, 2004), personality traits associated with dominance (Lukaszewski & Roney, 2009), the odour of dominant men (Havlicek, Roberts, & Flegr, 2005), and men's height (Pawlowski & Jasienska, 2005), have also been shown to occur in the follicular phase of the cycle. One possible explanation for shifts in judgements of masculinity and related traits across the menstrual cycle is that at mid-cycle, when conception risk is highest, cues to a man's condition or genetic quality are especially pertinent for women in order to make an adaptive mate choice. Masculine-faced men are thought to possess ‘good genes’ and to be healthier than relatively feminine-faced men (Thornhill & Gangestad, 2006), suggesting that a selective preference for masculinity when conception is possible could increase reproductive success. Indeed, masculinity has long been suggested to be an indicator of male quality (Folstad and Karter, 1992 and Thornhill and Gangestad, 1999), although there is limited evidence for this proposition (e.g. Scott, Clark, Boothroyd, & Penton-Voak, 2013). Nonetheless, masculine faces are not associated with traits that are desirable in a long term partner, such as investment (Boothroyd, Jones, Burt, & Perrett, 2007), meaning that a general preference for masculinity, even if it does reflect underlying genetic quality, may not be desirable. As such, cycle-dependent changes in line with a woman's conception risk, or current reproductive condition, could carry adaptive benefits. Irrespective of the logic for why such shifts occur, that cyclical changes in women's preferences for masculine traits occur suggests that within-individual variation in judgements, at least in part, are associated with hormonal variation. Indeed, existing work looking at other phases of hormonal transition across the female lifespan appears consistent with this idea. For example, circum-menopausal women show an increased preference for femininity in male and female faces relative to regularly cycling women (Jones et al., 2011, Little et al., 2010 and Vukovic et al., 2009). This finding may be explained by the reduced value placed on adaptive mate choice among circum-menopausal aged women. Specifically, circum-menopausal women may benefit less from choosing a masculine male partner since conception is no longer a relevant concern, and thus the advertised importance of genetic quality in men may be of diminished value. Moreover, increased preference for femininity in female faces may reflect lower levels of intrasexual competition, with women of this age achieving less from rival derogation relative to those of reproductive age. In other related work, Little et al. (2010) showed that post-pubescent girls had stronger preferences for masculinity in male faces than did younger peri-pubescent girls (see also Saxton, DeBruine, Jones, Little, & Roberts (2009), for similar results in both faces and voices). Together, these findings appear to suggest that attraction to masculinity is particularly high at times in which women are reproductively active. Advertisements of male quality may be most salient to women in the reproductive age group, particularly when fertile. While it is obvious that menarche, the menstrual cycle and the transition to menopause are related to major shifts in women's hormonal profiles, much research remains in determining which hormone, or group of hormones, mediate these changes in judgements of masculinity. Work by Welling et al. (2007) has previously documented a positive association between women's salivary testosterone and preference for male facial masculinity. This finding is consistent with much of the literature outlined above. For example, while effects are mixed, some research suggests very moderate testosterone increases occur near to ovulation in the follicular phase of the cycle (e.g. Alexander et al., 1990 and Dabbs, 1990; but see also: Schultheiss et al., 2003 and Welling et al., 2007) and indeed this is the time when women express enhanced masculinity preferences. Moreover, post-pubescent girls have higher levels of testosterone than peri-pubescent girls (e.g. Angold, Costello, Erkanli, & Worthman, 1999) and, while testosterone does not show a precipitous drop in the menopause, it does show a gradual age decline, meaning older women are likely to have lower levels of this hormone (Longcope et al., 1986 and Zumof et al., 1995). Therefore, the finding that testosterone positively relates to masculinity preferences is consistent with the pattern of results documented across these phases of female hormonal transition. Nonetheless, a range of other hormones, including oestrogen and progesterone, fluctuate across these reproductive life events. Thus, it is possible that several hormones, or interactions among hormones, underpin shifts in masculinity preferences that have been documented across the female lifespan. The current experiment investigated the impact of pregnancy and the post-partum period on women's preferences for feminized versus masculinized versions of both same-sex and opposite-sex faces. If variation in testosterone or other ovarian hormones contributes to masculinity preferences, pregnancy and the post-partum period may reflect further life stages wherein women's preferences for this trait change. It is known that testosterone levels increase throughout pregnancy and then drop swiftly post-partum (e.g. Buckwalter et al., 1999 and Leary et al., 1991). Given the results of Welling et al. (2007), discussed above, this may suggest that women would exhibit decreased preference for masculinity post-partum relative to pregnancy. Moreover, Watkins (2012) showed that masculinity preferences relate to measures of reproductive interest or ambition, and, if this is the case, we might further expect pregnancy and the post-partum to be associated with lower masculinity preferences than those exhibited by non-pregnant women of reproductive age. Notably, regularly cycling women have been shown to prefer greater levels of masculinity than women who use hormonal contraception (e.g. Jones et al., 2005 and Little et al., 2013). Pre-existing differences between oral contraceptive users and regularly cycling women may result in divergent differences when these groups’ preferences are compared to judgements made by pregnant and post-partum women. Thus, based on this previous research, we hypothesized that: (1) preferences for masculinity will be higher during pregnancy than post-partum; (2) preferences for masculinity during pregnancy and the post-partum period would differ from reports made by women using hormonal contraception or regularly cycling; (3) preferences for masculinity would be higher in regularly cycling women that those using hormonal contraception.
نتیجه گیری انگلیسی
Results 3.1. Preferences for male faces We first computed the mean masculinity preference scores for the ten male and female face pairs for participants when pregnant and in the post-partum period. We coded the selection of the feminine face in each pair as ‘zero’ and the selection of the masculine face as ‘one’. Thus, participants were assigned an overall score ranging from zero to ten, with higher scores indicating a greater preference for masculine faces. We similarly calculated the masculinity preferences among our group of nulliparous participants. Paired t-tests indicated that women preferred higher rates of masculinity in male faces than in female faces, a difference which was significant both when are participants were pregnant (t = 4.67, df = 25, p < .001) and in the post-partum phase (t = 2.63, df = 25, p = .015). Note that the sample for these analyses was somewhat reduced since there was missing data from 2 women's judgements of the female faces. This difference was also noted among our control sample of nulliparous women who were regularly cycling (t = 4.27, df = 32, p < .001) and among those who were using hormonal contraception (t = 9.88, df = 41, p < .001). Non-parametric tests of these differences revealed similar and significant effects. To test the impact of transitioning from pregnancy to the post-partum period on masculinity preferences, we conducted a linear-mixed model with reproductive state (pregnancy or post-partum) as the within-participant fixed factor and masculinity preference score obtained from the male faces as the dependent variable. The results of this test indicated a significant main effect of measurement time (F = 7.63, p = .01). Participants indicated a greater preference for masculine male faces during pregnancy (M = 6.15, S.E. = 49) relative to the post-partum phase (M = 4.89, S.E. = 49) ( Fig. 1). We then tested the main effect of participant age by adding this variable as a covariate to the model. Age did not have a significant main effect (F = .001, p = .98) on the model, and the main effect of reproductive state remained significant (F = 7.61, p = .01). Since previous research indicates differences in masculinity preferences related to use of hormonal contraception (e.g. Jones et al., 2005 and Little et al., 2013), we then re-ran this analysis adding whether or not the participant had begun to use hormonal contraception since the birth (yes/no, N = 9 had begun hormonal contraception) as a further fixed factor. In this model, the main effect of measurement time remained significant (F = 7.01, p = .01) and there was a main effect of contraceptive use in the post-partum phase (F = 8.55, p = .01), with women who used hormonal contraception preferring higher levels of masculinity. However, the interaction between measurement time and contraceptive use was non-significant (F = .44, p = .51). Thus, irrespective of use or non-use of hormonal contraception in the post-partum phase, women preferred lower levels of masculinity in male faces at this time relative to pregnancy. Mean (+S.E.) masculinity preference scores for assessments of male faces. ... Fig. 1. Mean (+S.E.) masculinity preference scores for assessments of male faces. Participants preferred significantly higher levels of masculinity in male faces when pregnant, compared to the post-partum period. Figure options We then examined how male facial masculinity preferences during pregnancy and post-partum compared to preferences reported by our nulliparous control sample. Since some women in our nulliparous group were using hormonal contraception, we compared regularly cycling and hormonal contraceptive using women as distinct control groups. When pregnant, our participants gave scores that fell between those given by regularly cycling and contraceptive using control participants, but were not significantly different from either (Mean difference = 1.14, S.E. = .74, p = .13; Mean difference = −.69, S.E. = .70, p = .33). In contrast to previous work, women using hormonal contraceptives preferred higher levels of masculinity in male faces than women who were regularly cycling (mean difference = 1.83, S.E. = .67, p < .01). Women's post-partum scores were significantly lower than those given by women who used hormonal contraception (mean difference = −1.94, S.E. = .70, p < .01), but did not differ from women who were regularly cycling (mean difference = −.11, S.E. = .74, p = .89) ( Fig. 2a). Masculinity preference scores for assessments of (a) male faces and (b) female ... Fig. 2. Masculinity preference scores for assessments of (a) male faces and (b) female faces. Shading reflects distinct groups of participants; note that the grey bars are repeated measures from the same individuals. In assessing male faces, women using hormonal contraception showed a greater preference for masculinity than regularly cycling women or women in the post-partum. In assessing female faces, women using hormonal contraception and women who were regularly cycling showed a lower preference for masculinity than pregnant and post-partum women. Figure options 3.2. Judgments of female faces Next, we re-ran the same tests described above, this time testing changes in preferences for masculinity in women's faces. The results of the linear-mixed model testing within-person shifts in masculinity preference from pregnancy to the post-partum phase indicated that there was no significant effect of measurement time on masculinity judgement (F = .009, p = .92). When participant age was added as covariate to the model it remained non-significant (F = .01, p = .92) and age did not have a main effect (F = .46, p = .50). Moreover, when we split the model based on women's hormonal contraceptive use status in the post-partum phase, the models were non-significant (non-users: F = 1.05, p = .35, Hormonal contraceptive users: F = .87, p = .36). Taken together, these results suggest that between-individual judgements of masculinity in female faces do not vary significantly across the transition from pregnancy to the post-partum ( Fig. 1). When we examined how pregnant and post-partum attractiveness judgements for masculinity in female faces differed from our control group of nulliparous women's scores, we found that pregnant women judged higher levels of masculinity as more attractive than women who were using hormonal contraception (mean difference = 1.60, S.E. = .59, p < .01). The difference between our pregnant participants judgements and that of the regularly cycling control group was non-significant (mean difference = .89, S.E. = .63, p = .16). Similarly, post-partum scores were significantly higher than scores given by hormonal contraceptive users (mean difference = 1.52, S.E. = .60, p = .01), but did not differ from women who were regularly cycling (mean difference = .81, S.E. = .63, p = .20). There was no difference in preferences between our control group of nulliparous women using hormonal contraception and nulliparous regularly cycling women (mean difference = −.71, S.E. = .55, p = .20) (See Fig. 2b).