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

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

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

4. Attractiveness, health + fertility

5. 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

6. 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

7. Why are symmetric faces attractive

8. 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

9. 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

10. 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) =

11. 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

12. 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

13. Problems for perceptual bias accounts

14. 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)

15. 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

16. 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

17. 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

18. 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

19. Hormonal profile and face preferences

20. 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

21. 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)

22. 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

23. 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

24. 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 ; no - DeBruine 2004)

25. GOOD LUCK ON THE EXAM
THANK YOU!
If you have any questions about the exam or the material please contact me

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