Revision lecture 2008

1. Revision lecture 2008

2. Exam formant Three questions in Section A Three questions in Section B You must complete one question from each section

3. Revision lecture outline Attractiveness & health Self-resemblance as a cue of kinship Why are symmetric faces attractive?

4. 1. Attractiveness & health Evolutionary Advantage account of attractiveness Proposes 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 it is true that 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

5. 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 Interpreting null findings is typically problematic 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.) Subsequent studies with same image-set found relationships between some attractive facial cues (e.g. averageness) and health measures

6. 1. Attractiveness & fertility Law Smith et al. 2006 (women) High levels of oestrogen and progesterone are associated with fertility among women and are positively related to women’s facial attractiveness (and attractive facial cues like perceived health + femininity) Penton-Voak et al. 2003 (women) Low (i.e. feminine) 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

7. 1. Attractiveness & fertility Roberts et al. 2004 (women) Late 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. 2003 (men) Facial 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

8. 1. Attractiveness & ‘good genes’ Roberts et al. 2005 (men) Heterozygosity 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

9. 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

10. 2. Self-resemblance as a cue of kinship Two biological theories predict that self-resemblance will influence attitudes to faces: Inclusive fitness theory: By helping kin you help your genes pass onto subsequent generations Inbreeding avoidance: By avoiding sex with kin you prevent deleterious effects of inbreeding on offspring [an alternative psychological account is ‘mere exposure’ - self-resembling faces are familiar and therefore ‘liked’]

11. 2. Self-resemblance as a cue of kinship Trusting behavior (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)

12. 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)

13. 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!

14. 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)

15. 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 the 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

16. 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 in a non-mating context (e.g. increases perceived trustworthiness of other-sex faces) Consistent with inbreeding avoidance explanation of attitudes to self-resembling faces, 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 acts as a cue of kinship and is difficult to explain in terms of attitudes to familiar stimuli (i.e. hard to explain in terms of ‘mere exposure’ effects)

17. Symmetry is attractive (Perrett et al 1999) When the symmetry of faces is increased using computer graphic methods, this increases it’s attractiveness - why? Evolutionary advantage account (Thornhill & Gangestad 1999) Symmetry is attractive because it signals health + fertility Simple perceptual bias account (Mach 1887) Symmetry is attractive because symmetric because the human visual system is particularly sensitive to bilateral symmetry Prototype-based perceptual bias accounts (Enquist et al 2002) Symmetric faces are attractive because they resemble prototypical mental representations of faces Conclusions Although there is evidence perceptual bias can cause symmetry preferences, perceptual bias accounts cannot explain human’s symmetry preferences 3. Why are symmetric faces attractive?

18. Evidence for Perceptual Bias Symmetry preferences seen in: • objects • decorative art Rensch, 1963 Gombrich, 1984 Original Symmetrical These effects suggest there may be nothing ‘special’ about facial symmetry that is attractive - consistent with view preferences for symmetric faces are a ‘trick’ of the visual system Original Symmetrical

19. Neural Networks & Perceptual Bias • Computer programs trained on stimuli for recognition • Show that recognition training can create preference (recognition) for symmetry Enquist & Arak, 1994, Nature Training Set Johnstone, 1994, Nature Novel symmetric stimuli preferred (most reaction) =

20. Prototypes and Perceptual Bias • Train chickens to discriminate between rewarding and non-rewarding stimuli • Stimuli were two asymmetric crosses which were mirror images of each other Both associated with reward Jansson et al., 2002, Anim Behav

21. Prototypes and Perceptual Bias PECK! • Train chickens to discriminate between rewarding and non-rewarding stimuli • On subsequent testing chickens preferred novel symmetric cross to either asymmetric cross • So symmetry preference can arise as by-product of visual system & experience Novel symmetric cross Jansson et al., 2002, Anim Behav

22. Perceptual bias accounts cannot accommodate individual differences in symmetry preferences Attractive women like symmetric male faces more than relatively unattractive women do Little et al (2001)

23. Perceptual bias accounts cannot accommodate sex-specific symmetry preferences Female judges(Little et al., 2001) NB - symmetry attractive in BOTH male and female faces but MORE attractive in opposite-sex than own-sex faces

24. Perceptual bias accounts cannot accommodate greater symmetry preferences in mate choice relevant stimuli Little & Jones, 2003, Proc Royal Soc

25. Symmetry and attractiveness in other modalities • Symmetric individuals have attractive voices • (Hughes et al., 2002) • Symmetric individuals have attractive body odours • Rikowski & Grammer (1998) These effects suggest symmetry signals an attractive underlying quality

26. Evidence for perceptual bias accounts Symmetry preferred in art Evidence for prototype preference (in chickens and neural net.) Problems for perceptual bias account Individual differences in symmetry preferences Opposite-sex face advantage Upright face advantage Also - symmetry attractive independent of prototypicality (Rhodes et al.) Also - symmetry predicts attractiveness in other (non-visual) modalities Conclusions There is evidence perceptual bias can cause symmetry preferences BUT Perceptual bias accounts cannot explain human’s symmetry preferences

27. Good luck in the examhappy holidays