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Revision lecture. Two key topics covered today 1. Relationship between facial attractiveness and health 2. Strategic variation in masculinity preferences (cyclic shifts and condition-dependent preferences). The relationship between facial attractiveness and measures of health.
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Two key topics covered today 1. Relationship between facial attractiveness and health 2. Strategic variation in masculinity preferences (cyclic shifts and condition-dependent preferences)
The relationship between facial attractiveness and measures of health
The relationship between facial attractiveness and measures of health Why is this an important issue? Studies showing high agreement in face preferences among people of diverse ages (Slater & Kirby 1998) or from diverse cultures (Perrett et al. 1994, 1998; Rhodes et al. 2001) suggest that attractiveness has a biological basis. Evolutionary advantage accounts of attractiveness One possibility is that, because mating with healthy individuals will increase reproductive success, attractiveness judgements are psychological adaptations that promote mating with healthy individuals (Miller & Todd 1998; Thornhill & Gangestad 1999). So, what’s the problem? A strong prediction of this evolutionary account of attractiveness is a link between attractiveness and health (though some researchers have suggested that antibiotics etc. may mask this relationship in modern societies, e.g. Thornhill & Gangestad 1999). However, some researchers have suggested that there is very little evidence for such an association and that this lack of evidence undermines the evolutionary advantage account of attractiveness (e.g. Enquist et al. 2002; Kalick et al. 1998).
The relationship between facial attractiveness and measures of health Three different ‘types’ of study that have investigated this issue 1. Past health problems: Some studies have tested for a negative correlation between incidence of past health problems and ratings of facial attractiveness. 2. Genetic markers of a strong immune system: Some studies have tested for differences in facial attractiveness of individual with genetic markers of a strong immune system and those with genetic markers of a relatively weak immune system. 3. Fertility and reproductive health: Some studies have tested for a positive relationship between indices of reproductive health or fertility and facial attractiveness.
The relationship between facial attractiveness and measures of health Past health problems and facial attractiveness Kalick et al. (1998) conducted arguably the first systematic study of the possible link between facial attractiveness and measures of long-term health in humans. A ‘health score’ was derived from medical professionals assessments of the health of individuals based on their medical records. Ratings of the facial attractiveness of those individuals were not correlated with this ‘health score’. Interpreted as strong evidence against the evolutionary advantage view of attractiveness (and widely cited as such). Problems with the study: Low resolution, blurry, black and white photographs were used for ratings. Photographs and medical records rather ‘old fashioned’. Always problematic to interpret null findings.
The relationship between facial attractiveness and measures of health Past health problems and facial attractiveness Some subsequent studies have found that self-reported incidence of past health problems is negatively related to facial attractiveness ratings, in women at least (e.g. Hume & Montgomerie 2001). Other studies have found that attractive facial characteristics (such as femininity in women’s faces, Thornhill & Gangestad 2006) are negatively correlated with incidence of past health problems, even when using the same set of images as Kalick et al. (e.g. facial averageness, Rhodes et al. 2001). The null finding in Kalick et al. (1998), although widely cited as evidence aginst evolutionry advantage accounts of attractiveness, is difficult to reconcile with these findings. Studies using this method to assess the relationship between attractiveness and health generally rely on self-report data or subjective evaluations of medical records. What about more objective indices of health used in medical research?
The relationship between facial attractiveness and measures of health Genetic markers of a strong immune system The major histocompatability complex (MHC) is a gene complex that codes for the strength of immune system responses. Individuals with heterozygous MHC typically have more effective immune system responses than do individuals with homozygous MHC and, consequently, are better able to fight disease and infection. In other words, MHC heterozygosity is a good index of immune system function. Roberts et al. (2005) demonstrated that the faces of men with heterozygous MHC were judged to be significantly more attractive and healthy-looking than those of men with homozygous MHC. Equivalent findings were also observed for attractiveness and health ratings of ‘skin patches’. Lie et al. (2008) recently replicated this effect of MHC heterozygosity in a different sample of men. In a sample that was more diverse in terms of age and ethnicity, Thornhill et al. (2003) observed no relationship between MHC heterozygosity and attractiveness.
The relationship between facial attractiveness and measures of health Reproductive health and facial attractiveness Women’s attractiveness Low waist-hip ratio (i.e. a curvy, attractive body shape) is a good predictor of women’s reproductive health and is correlated with women’s attractiveness (Penton-Voak et al. 2003). Face photographs taken during the most fertile phase of the menstrual cycle (i.e. around ovulation) are judged more attractive than those taken during the mid-luteal (i.e. low fertility) phase (Roberts et al. 2004). Men’s attractiveness Sperm count and mobility are positively correlated with ratings of men’s facial attractiveness (Soler et al. 2003), although one subsequent study did not replicate this finding (Peters et al. 2008). There is some good evidence for an association between fertility indices and women’s attractiveness, though findings are more mixed for men.
The relationship between facial attractiveness and measures of health Other types of evidence The studies discussed thus far present evidence from direct tests for a link between health and attractiveness, However, that’s not the only type of evidence for such an association. For example, that women with attractive faces also tend to have attractive voices (Feinberg et al. 2005) and attractive body odours (Rikowski & Grammer 1998) is also consistent with this view and hard to otherwise explain. Conclusion Although Enquist et al. (2002) suggested that there is little evidence for an association between facial attractiveness and health, this proposal does not do justice to the literature. Findings using objective measures of health present some compelling evidence for a correlation between health and attractiveness, particularly with regard to MHC heterozygosity and men’s facial attractiveness.
Cyclic shifts in women’s preferences for facial masculinity
Cyclic shifts in women’s preferences for facial masculinity Masculinity in men’s faces is associated with good long-term health (Thornhill & Gangestad 2006), but masculine men are perceived as dishonest and ‘bad parents’ (Perrett et al. 1998). Femininity in men’s faces is associated with poor long-term health (Thornhill & Gangestad 2006), but feminine men are perceived as honest and ‘good parents’ (Perrett et al. 1998).
Cyclic shifts in women’s preferences for facial masculinity ‘Trade off’ theory and women’s preferences for masculine men (Penton-Voak et al. 1999) Choosing a masculine mate will confer some benefits to the woman (e.g. increased offspring health via mating with healthy male). However, women may also incur costs if they choose a masculine mate (e.g. increased risk of desertion, low investment etc.) Thus, when assessing men’s attractiveness, there is a trade off between the possible costs and benefits of choosing a masculine or feminine partner. Strategic variation in preferences may allow women to resolve this trade-off and maximise the possible benefits of their mate choices. Since feminine men are perceived to possess traits that are desirable in a long-term partner (e.g. honesty, ‘good parent’), general preferences for relatively feminine men as long-term partners may be optimal. However, this would be to the detriment of offspring health, unless women are more open to mating with masculine short-term partners around ovulation than at other times.
Cyclic shifts in women’s preferences for facial masculinity Evidence for cyclic shifts in women’s preferences for masculine men Many studies have demonstrated that women show stronger preferences for masculine male faces around ovulation than at other times (e.g. Jones et al. 2005; Penton-Voak et al. 1999), particularly when partnered women judge men’s attractiveness as short-term (extra-pair) partners. This cyclic shift in women’s preferences for masculine men is not unique to judgements of men’s facial attractiveness. It has also been observed for women’s masculinity preferences when judging the attractiveness of men’s voices (Feinberg et al. 2006), bodies (Little et al. 2007) and behavioral displays (Gangestad et al. 2004). Other studies have shown that this cyclic shift is also not specific to attractiveness judgements, finding that women may be more attentive to male faces generally around ovulation than at other times (as indicated by faster sex-classification of male, but not female, faces around ovulation, Macrae et al. 2002). Women’s perceptions of men are correlated with changes in fertility during the menstrual cycle in ways that are consistent with ‘trade off’ theories of attraction.
Cyclic shifts in women’s preferences for facial masculinity Converging evidence for proposed function of cyclic shifts in masculinity preferences Cyclic shifts in women’s preferences for masculine men are proposed to function to maximise the benefits of women’s mate preferences, potentially promoting bonding with feminine ‘caring sharing’ men as long-term partners, while increasing offspring health via extra-pair mating with masculine men around ovulation (Penton-Voak et al. 1999). A string prediction of this proposed function is that partnered women’s attitudes to their romantic partners should also change during the menstrual cycle in ways that parallel cyclic shifts in masculinity preferences. Consistent with this latter proposal, women report more frequent sexual fantasy about men other than their primary partner around ovulation than at other times (but report no equivalent cyclic change in frequency of sexual fantasy about their partner, Gangestad et al. 2002). Additionally, Jones et al. (2005) found that women reported lower commitment to their partner around ovulation than at other times (but found no equivalent cyclic shift in women’s happiness with their relationship). Other studies have found that women are more likely to, e.g., go out without their romantic partner around ovulation than at other times (Haselton & Gangestad 2006).
Cyclic shifts in women’s preferences for facial masculinity Possible hormonal mechanisms While early studies of cyclic shifts in women’s masculinity preferences and other behaviours focused on establishing a link between cyclic variation in fertility and behaviour, fertility in and of itself cannot be a mechanism for these cyclic shifts (Jones et al. 2005). Consequently, more recent studies have investigated the hormonal changes that might be most closely linked to cyclic shifts in women’s masculinity preferences. To date studies have been rather mixed. Jones et al. (2005) and Puts (2006) emphasized the effects of changes in progesterone level for cyclic variation in masculinity preferences, though other studies (e.g. Roney & Simmons 2008) have emphasized the possible effect of oestrogen. A more recent study (Welling et al. 2007), however, found no effect of oestrogen, a small effect of progesterone (which was more complex than that observed by Jones et al. and Puts) and a relatively large effect of testosterone level. Hormone-mediated face preferences are not unique to women. Welling et al. (2008) found that men’s preferences for femininity in women’s faces were stronger when their testosterone levels were high than when their testosterone levels were relatively low.
Condition-dependent masculinity preferences Condition-dependent mate preferences in non-human species (Bakker et al. 1999) Male stickelback signal their health via the redness of the coloring on their throat (healthier males have redder throats). By contrast, female stickelback signal their health by their body weight (healthier females are heavier). Bakker et al. (1999) found that, although females generally prefer males with particularly red throat coloring, heavier females were significantly more likely to demonstrate this preference than underweight females were. Such variation in mate preferences that are predicted by indices of the chooser’s own condition are often referred to as ‘condition-dependent’ preferences. Condition-dependent preferences are thought to function to ensure that mating effort is allocated efficiently.
Condition-dependent masculinity preferences Condition-dependent masculinity preferences The ‘trade off’ in women’s masculinity preferences that is thought to underpin cyclic shifts in women’s face preferences also is relevant to condition-dependent preferences. Masculine men may be ‘risky’ partner choices as they are perceived as possessing antisocial traits (Perrett et al. 1998). However, masculine men are desirable mates in other ways because they are particularly health (Thornhill & Gangestad 1999). Women’s own physical condition may affect how they resolve this this trade off in predictable ways (Little et al. 2001; Penton-Voak et al. 2003). For example, attractive, healthy women may be better able to attract and/or retain high quality (masculine, symmetric) men as long-term partners compared with relatively unattractive, unhealthy women (Little et al. 2001; Penton-Voak et al. 2003). Indeed, Little et al. (2001) found that women who rated themselves as particularly attractive demonstrated stringer preferences for masculine and symmetric men as long-term partners than did women who considered themselves to be relatively unattractive. Additionally, Penton-Voak et al. (2003) replicated these findings for masculinity preferences using more objective measures of women’s attractiveness (waist-hip ratio and other-rated facial attractiveness).
Condition-dependent masculinity preferences Condition-dependent masculinity preferences in women These findings have been extended in more recent work: Jones et al. (2005) found that indices of women’s physical condition (waist-hip ratio) and psychological condition (anxiety, stress and depression measures) independently predicted women’s preferences for healthy-looking male, but not female, faces in ways consistent with condition-dependent preferences. Vukovic et al. (2008) found that self-rated attractiveness predicted women’s preferences for masculinity in men’s voices when the voice recordings were played forwards, but not when the voice recordings were played backwards (suggesting the effect of self-rated attractiveness on preferences for masculine sounds does not occur unless the pitch-manipulation is applied to speech). Condition-dependent preferences are an excellent example of applying models of mate preferences based on behaviour in a non-human animal species to generate novel hypotheses about human mate preferences. They are also an excellent example of how human mate preferences can show individual differences, which are evidence against (so-called) ‘universal’ preferences.
