Revision lecture 2006

Revision lecture outline

1. Attractiveness & health

2. Self-resemblance as a cue of kinship

3. Hormone-mediated face preferences (cyclic shifts, pregnancy)

4. Condition-dependent face preferences

1. Attractiveness & health

Evolutionary Advantage account of attractivenessProposes that attractiveness judgments reflect adaptations that promote choice of healthy partners (Thornhill & Gangestad, 1999)

i.e. facial attractiveness signals aspects of health (e.g. fertility, low number of past health problems, ‘healthy’ genetic profile)

BUT - many researchers have challenged this proposal, noting that there is little evidence to support this view (e.g. Enquist et al. 2002; Kalick et al. 1999; Valentine et al. 2004)

While early studies of the link between attractiveness and actual health were not encouraging, more recent studies (with improved measures of health) present a different picture

1. Attractiveness & health

Kalick et al. (1999)Tested for a positive correlation between incidence of past health

problems (assessed from medical records) and attractiveness

No relationship observed

BUT - some problems with this study

1. Interpreting null findings is typically problematic

2. Face stimuli were low resolution B&W photographs (and some later studies suggest skin quality may play important role in attractiveness-health relationship, e.g. Roberts et al.)

3. Subsequent studies with same image-set found relationships between some attractive facial cues (e.g. averageness) and health measure

1. Attractiveness & fertility

Law Smith et al. 2006High levels of oestrogen and progesterone are associated with fertility among women and are positively related to women’s facial attractiveness

Penton-Voak et al. 2003Low waist-hip ratio is associated with fertility among women and is associated with attractive facial appearance

Both findings support the view that attractiveness in women signals reproductive health

1. Attractiveness & fertility

Roberts et al. 2004Late follicular phase of menstrual cycle (i.e. around ovulation) is most fertile phase

Women’s faces more attractive around ovulation than at other times

Soler et al. 2003Facial attractiveness in men is associated with good semen quality (i.e. higher sperm count and better sperm mobility)

Both findings support link between attractiveness and fertility

1. Attractiveness & ‘good genes’

Roberts et al. 2005Heterozygosity at the MHC complex (genes that code for immunity to infectious diseases) associated with strong immune system

Heterozygotes judged more attractive than homozygotes

Heterozygotes have healthier-looking facial skin than homozygotes

Although Thornhill et al. (2003) found no link between MHC heterozygosity and men’s facial attractiveness, they did not control for age of men or ethnicity

1. Attractiveness & health

Conclusions

Although there is little evidence that facial attractiveness is associated with (low) frequency of past health problems, recent findings for links between attractiveness and more objective/rigorous measures of fertility (e.g. measured hormone levels, semen quality) and measures of immune system strength (MHC heterozygosity) present compelling evidence that facial attractiveness is a cue to various aspects of health

2. Self-resemblance as a cue of kinship

Two theories predict that self-resemblance will influence attitudes to faces:

1. Inclusive fitness theory: By helping kin you help your genes pass onto subsequent generations

2. Inbreeding avoidance: By avoiding sex with kin you prevent deleterious effects of inbreeding on offspring

2. Self-resemblance as a cue of kinship

Trusting (DeBruine, 2002)

Tested for effects of self-resemblance of other same-sex players in an economic ‘trust’ game

People more likely to behave in trusting fashion towards self-resembling players than other-resembling players

Supports key prediction of inclusive fitness theory (trust kin more than non-kin)

2. Self-resemblance as a cue of kinship

Attractiveness in own- and other-sex faces

(DeBruine, 2004)

Tested for effects of self-resemblance on preferences for own- and other-sex faces

Self-resemblance increased attractiveness of own-sex faces (promoting affiliation with own-sex kin)

Self-resemblance did not increase attractiveness of other-sex faces to the same extent (reducing likelihood of inbreeding)

2. Self-resemblance as a cue of kinship

‘Trustworthy not lustworthy’ (DeBruine, 2005)

Previous findings suggested that self-resemblance in other-sex faces increases trusting but not attractiveness

Self-resembling other-sex faces are 1) perceived as trustworthy, 2) unattractive for short-term relationships (e.g. one-night stands)

and 3) ‘neutral’ in terms of attractiveness for long-term relationships

Again, suggests that self-resemblance is a cue of kinship - trust kin but don’t sleep with them!

2. Self-resemblance as a cue of kinship

Children’s faces (DeBruine, 2004)

DeBruine found self-resemblance increased positive attitudes for judgments of children’s faces (again, positive attitudes to kin)

Children’s faces are obviously not potential mates, so findings consistent with claim that self-resemblance preferred in faces of

individuals who are not potential mates (or when faces judged out with mating context)

Various studies by Platek found the above effect more pronounced in men than women (no sex difference in DeBruine)

2. Self-resemblance as a cue of kinship

Attitudes to self-resemblance

Increased preference for self-resembling faces when raised progesterone level prepares body for pregnancy (DeBruine, Jones & Perrett, 2005)

That effect is most pronounced for female faces suggests the effect reflects increased preference for sources of support and care than mechanism for avoiding inbreeding

Indeed, change in preference for self-similar faces related to progesterone level NOT conception risk

2. Self-resemblance as a cue of kinship

Conclusions

People appear to use self-resemblance as a cue of kinship when judging others

Consistent with inclusive fitness theory, self-resemblance increases positive attitudes when ‘target’ is not a potential mate (e.g. children and same-sex individuals) or when other-sex faces are judged out with mating context (e.g. increases perceived trustworthiness of other-sex faces)

Consistent with inbreeding avoidance, self-resemblance decreases attractiveness of potential mates when judged for an explicitly sexual relationship (e.g. a one night stand)

That attitudes to self-resemblance are sensitive to the context (I.e. the ‘question’ asked) and face-type (child, own-sex, other-sex) in these ways supports the view that self-resemblance is a cue of kinship and are difficult to explain in terms of attitudes to familiar stimuli

3. Hormone-mediated attraction

Masculinity preferences (Penton-Voak et al 1999)Cost to preferring masculine men:

Anti-social personality traits + low investment (Perrett et al. 1998)

Benefit to preferring masculine men (handicap hypothesis):

Good genes for offspring health (Thornhill & Gangestad, 1999)

Women may maximize the benefits of their mate preferences by preferring feminine men generally but being more attracted to masculine men around ovulation (when most fertile) - particularly pronounced when partnered women judge unfamiliar men for short-term relationship (i.e. possible EPC)

Similar effects seen for voice preferences (Feinberg et al. 2006)

3. Hormone-mediated attraction

Attitudes to romantic partner and cycle phaseIf cyclic shifts in women’s preferences for masculine men reflect an adaptation for securing good genes for immunocompetence within long-term relationship with feminine, ‘caring sharing’ man, then attitudes to long-term partner should also change around ovulation

Increased incidence of sexual fantasy about men other than primary partner around ovulation (Gangestad et al. 2002)

Reduced commitment to romantic partner around ovulation, but no change in happiness with relationship (Jones et al. 2005)

3. Hormone-mediated attraction

Attitudes to self-resemblance

Increased preference for self-resembling faces when raised progesterone level prepares body for pregnancy (DeBruine, Jones & Perrett, 2005)

That effect is most pronounced for female faces suggests the effect reflects increased preference for sources of support and care than mechanism for avoiding inbreeding

Indeed, change in preference for self-similar faces related to progesterone level NOT conception risk

3. Hormone-mediated attraction

Contagion avoidance (Jones et al. 2005)

Increased aversions to possible sources of contagion (e.g. meat) observed during early pregnancy thought to reflect mechanism for

protecting developing fetus and mum-to-be

Increased aversion to unhealthy faces during pregnancy, luteal phase of menstrual cycle and following oral contraceptive use (all

high progesterone conditions)

Increased aversion to unhealthy faces also associated with raised progesterone during menstrual cycle

3. Hormone-mediated attraction

ConclusionsAlthough we tend to think of people having ‘types’ that they find attractive (i.e. tend to think of preferences as stable within an

individual), these findings show that changes in hormone levels are associated with predictable changes in face preferences

Although it is now well established that face preferences change systematically during the menstrual cycle, the hormonal mechanisms that cause this remain poorly understood

Most previous studies have emphasized the likely importance of changes in progesterone level, but other hormones are probably

also important (e.g. testosterone level)

4. Condition-dependence

Stickleback (Bakker et al. 1999)

Male stickleback signal good health via red throat patch and males with red throat patches are preferred

Heavy female stickleback are healthier than lighter stickleback and have the strongest preferences for healthy males

Adaptive behavior if healthy females are better able to compete for healthiest mates

4. Condition-dependence

Condition-dependent health preferences among women (Jones et al. 2005)

Low waist-hip ratio (WHR) signals health in women

- Women with low WHR have stronger preferences for apparent health in men’s (but not women’s) faces than women with higher WHRs do

- Low stress and anxiety among women also associated with increased preference for male apparent health

These findings are analogous to condition-dependent preferences seen in stickleback

4. Condition-dependence

Masculinity preferences

Cost to preferring masculine men as long-term partners: Anti-social personality traits + low investment (Perrett et al. 1998)

Women with high SRA (Little et al. 2001), high other-rated facial attractiveness or low WHR (Penton-Voak et al. 2003) have stronger preferences for masculine men as long-term partners than do relatively unattractive women

Attractive women better able to offset possible costs of choosing a masculine long-term partner?

4. Condition-dependence

Different from matching hypothesis

Matching hypothesis suggests that people take into account their own attractiveness when choosing a

romantic partner ONLY when there is a possibility of being rejected (i.e. not on face preference tests)

However, findings for condition-dependent face preferences show that own attractiveness can modulate

face preferences even when there is no possibility of rejection

Good luck in the exam