PS4029/30 Perspectives on social attributions Lecture 12 [key themes] May 2005

EXAM FORMAT 1 question from Section A (choice from 3 questions) + 1 question from Section B

Attractiveness, health + fertility Why are symmetric faces attractive? Hormonal profile and face preferences Attitudes to self-resemblance in faces

Attractiveness, health + fertility

Why might facial attractiveness signal health & fertility Humans and non-humans might increase their reproductive success by choosing healthy, fertile mates Attractiveness judgments may be psychological adaptations that identify healthy, fertile mates This is often called the ‘evolutionary advantage’ account of face preferences [Thornhill and Gangestad, 1999] The issue has been investigated in 3 ways: Incidence of illness Genetic heterozygosity (healthy genetic profile) Measures of fertility

Past health problems (Kalick et al 1998) no relationships between facial attractiveness + medical records [but used only BW images] Genetic heterozygosity Hetrozygotes had healthier, attractive skin (Roberts et al 2005) No link with facial attractiveness (Thornhill et al 2003) [but Thornhill had diverse age range of faces] Fertility Women’s faces more attractive around ovulation (Roberts et al., 200?) Women with low WHR have attractive faces (Penton-Voak et al., 2003) Men with healthy sperm have attractive faces (Soler et al 2003) **NEW REF** Women with high levels of oestrogen have attractive, feminine, healthy faces (Law Smith et al. 2005) [hi oestrogen=actually fertile, healthy] Conclusion Evidence that facial attractiveness = medical health is mixed The most tightly controlled study did find effects however (Roberts et al., 2005) Evidence that facial attractiveness is related to fertility is more compelling These findings support the evolutionary advantage view of attractiveness

Why are symmetric faces attractive

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

Evidence for Perceptual Bias Symmetry preferences seen in: objects decorative art Rensch, 1963 Gombrich, 1984 Original Symmetrical Large literature showing in a wide variety of animals show preferences for symmetry. 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

Neural Networks & Perceptual Bias Computer programs trained on stimuli for recognition Show that recognition training can create preference (recognition) for symmetry Training Set Enquist & Arak, 1994, Nature Large literature showing in a wide variety of animals show preferences for symmetry. Johnstone, 1994, Nature Novel symmetric stimuli preferred (most reaction) =

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 Large literature showing in a wide variety of animals show preferences for symmetry. Both associated with reward Jansson et al., 2002, Anim Behav

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 Large literature showing in a wide variety of animals show preferences for symmetry. Novel symmetric cross Jansson et al., 2002, Anim Behav

Problems for perceptual bias accounts

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)

Female judges (Little et al., 2001) 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

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

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

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 is attractive independent of prototypicality Also - symmetry predicts attractiveness in other modalities Conclusions There is evidence perceptual bias can cause symmetry preferences BUT Perceptual bias accounts cannot explain human’s symmetry preferences

Hormonal profile and face preferences

Studies have emphasised high agreement on attractiveness More recently, studies have explored individual differences in face preferences Hormonal profile influences women’s preferences for Sexual dimorphism (masculine faces preferred most when fertile) Health appearance (aversion to illness strongest when pregnant) Self-resemblance (aversion to self strongest when fertile) Conclusion Systematic variation in face preferences due to changes in hormonal profile support an evolutionary advanatge view of attractiveness as they: Maximise the benefits of women’s mate choices (e.g. masculinity) Compensate for maternal immunosupression/protect fetus Promote close ties with family when body prepares for pregnancy and avoid inbreeding

There are costs associated with choosing a masculine long-term partner Menstrual cycle and change in masculinity preference (Penton-Voak et al 1999) Women are more attracted to masculine faces when fertile (late follicular phase) Why? Choosing a masculine mate increases offspring health (Thornhill & Gangestad, 1999) BUT There are costs associated with choosing a masculine long-term partner - perceived as ‘cold’ and ‘bad parent’ (Perrett et al 1998) - aggressive and unfaithful (Mazur & Booth 1998) Women may maximise the benefits of their mate choices by preferring feminine males as long term partners but being more open to masculine men when fertile (Penton-Voak et al 1999) Consistent with this, women with partners report being less committed to their relationships around ovulation (when fertility is high) (Jones et al 2005)

Pregnancy and change in aversion to illness cues (Jones et al 2005) Pregnant women avoid foods that may be contaminated with disease Does hormonal profile alter aversion to facial cues associated with illness? Pregnancy, pill use and the luteal phase of the menstrual cycle are associated with high progesterone level Pregnancy, pill use and the luteal phase of the menstrual cycle are also associated with increased aversion to faces with pallor (i.e. unhealthy faces) Increased contagion avoidance during pregnancy (or when the body prepares for pregnancy) will compensate for maternal immunosupression and protect the developing fetus

Menstrual cycle and attraction to kinship cues (i. e Menstrual cycle and attraction to kinship cues (i.e. facial self resemblance) DeBruine et al 2005 Inbreeding reduces offspring health Family are likely sources of help and care during pregnancy Aversion to self resemblance in faces is strongest when fertile Attraction to self resemblance is strongest when raised progesterone prepares the body for pregnancy (i.e. luteal phase) These changes in preferences will promote affiliation with family during pregnancy and reduce risk of inbreeding

Attitudes to self resemblance Pro-social regard for self-resembling individuals will help kin (Hamilton 1964) Aversion to self-resemblance in mating context will avoid cost of inbreeding (Bittles & Neel 1994) DeBruine 2005 (opposite-sex faces only) People show aversion to self for short-term contexts (sexual attraction) People show preferences for self when judging trust No effect of self for long-term context (mix of trust + sexual attraction) DeBruine 2004 (same- and other-sex faces) People are attracted to self in own-sex faces but not opposite-sex faces Self looks ‘average’ for both own- and other-sex faces DeBruine 2004 Self is attractive in infants - debate about whether this effect more pronounced for men than women (yes - Platek 2002 2003; no - DeBruine 2004)

GOOD LUCK ON THE EXAM THANK YOU! If you have any questions about the exam or the material please contact me ben.jones@abdn.ac.uk

EXAM FORMAT 1 question from Section A (choice from 3 questions) + 1 question from Section B