1. PS4029/30 Perspectives on social attributions
Lecture 4
Feb 2005

2. Lecture 3: Evolutionary advantage accounts of symmetry preferences
Accounts of sym preferences (recap)
Does symmetry signal mate quality?
Is symmetry particularly attractive in mate choice relevant stimuli?
Is symmetry attractive independent of prototypicality?
Symmetric individuals are not only visually attractive

3. 1. Perceptual bias accounts (recap)
Symmetry is attractive because :
- symmetric stimuli of any kind are processed more easily by the visual system
than relatively asymmetric stimuli
- as a byproduct of the tendency for symmetric objects to be prototypical

4. 1. Evolutionary advantage view
Symmetry is attractive because of advantages associated with choosing a symmetric mate

5. Non-Human Species Preferences for Symmetry
Female barn swallows prefer males with symmetrical tail feathers
Female Zebra finches prefer symmetrical males
Møller, 1994, Anim Behav
Large literature showing in a wide variety of animals show preferences for symmetry.
Swaddle & Cuthill, 1994, Nature

6. 2. Does symmetry signal mate quality?
An important component of the evolutionary advantage view is
that symmetry may signal qualities that are desirable in a mate
(e.g. health, fertility)
[e.g. Thornhill & Gangestad, 1999]
This a hugely controversial issue but there have been some
positive relationships reported between symmetry and ‘mate
quality’

7. Symmetry and Quality Controversial area (Enquist et al., 2002)
Non-humans
Symmetry associated with ejaculate quality in 3 ungulates (hoofed animals)
Antler symmetry positively related to immune measures in reindeer
Humans
Body symmetry positively related to sperm number per ejaculate and sperm speed
Breast symmetry positively correlated with fecundity
Gomendio et al., 2000, Proc Royal Soc
Lagesen & Folstad, 1998, Behav Ecol Sociobio
Manning et al., 1998, Evo Human Behav
Møller et al., 1995, Ethol. Sociobio

8. Symmetry and Quality II
Humans
facial symmetry positively related to intelligence
(Zebrowitz et al., 2000)
Body symmetry positively related to athletic ability (Manning et al., 1998)
Facial symmetry positively related to masculinity
(another putative cue to immunesystem strength, Gangestad & Thornhill, 2003)
[we’ll return to the issue of masculine facial
proportions as a signal of immunity to infection in lecture 7]

9. Perceptual bias views don’t
3. Is symmetry particularly attractive in mate choice relevant stimuli?
Evolutionary advantage view emphasises importance of symmetry for ‘mate preferences/choices’
Perceptual bias views don’t

10. The Mona Lisa

11. Eyes and mouth inverted
The Thatcher Illusion
Eyes and mouth inverted

12. Symmetry Preferences in Upright and Inverted Faces
Inversion disrupts normal face processing - inverted faces are processed more like visual objects than faces
In regard to symmetry preference:
A simple perceptual bias view suggests symmetry preference should be constant across orientation about a vertical axis
Evolutionary Advantage view suggests symmetry particularly attractive in upright faces
Murray, Yong, & Rhodes, 2000, Psych Sci

13. Symmetry Preference in Upright and Inverted Opposite-Sex Faces
Little & Jones, 2003, Proc Royal Soc

14. 4. Is symmetry attractive independent of prototypicality?
Central to the perceptual bias account is the notion that symmetry preferences are an artifact of preferences for prototypicality
Evolutionary bias makes no such claim

15. Symmetry in Familiar Faces
Symmetric Asymmetric
Even though symmetric version is less familiar (and less prototypical), symmetry is still preferred - Little and Jones, 2003)

16. Symmetry and prototypicality
Ratings of the attractiveness of faces and ratings of their
distinctiveness (inverse of averageness) are -vely correlated
Ratings of the attractiveness of faces and symmetry are +vely
correlated
correlated when effects of distinctiveness are controlled using
a partial correlation design
Symmetry attractive independent of averageness
(Rhodes et al., 1999)

17. 5. Symmetric individuals are not only visually attractive
Perceptual bias account proposes that symmetry
preferences are a byproduct of the visual system
Evolutionary advantage view proposes that symmetry is
attractive because it signals an important underlying
quality (e.g. health)
Does symmetry predict attractiveness when you can’t see it?
Perceptual bias: NO (visual system needs symmetry as input)
Evolutionary advantage: YES (underlying quality also reflected in
other ways)

18. Prototype faces tend towards very high symmetry
Composites of symmetric faces more attractive than
composites of asymmetric faces (Penton-Voak et al., 2001)
Supports evolutionary advantage view (must be correlates of
symmetry that are causing effect below because symmetry
not visible)
Judged:
Unattractive
Unhealthy
Unfit
Judged:
Attractive
Healthy
Fit
Composite of
asymmetric faces
Composite of
symmetric faces

19. Symmetry and attractiveness in other modalities
Symmetric individuals have attractive voices
(Hughes et al., 2002)
Symmetric individuals have attractive body odours
[NB - in men this effect only emerges when female judges are in late follicular, fertile phase of menstrual cycle]
Rikowski & Grammer (1998)

20. Lecture 4 Key Themes
1. That symmetry advertises qualities that are attractive in potential mates
Is consistent with Evolutionary Advantage view
2. That symmetry is more attractive in mate-choice relevant stimuli than
Other classes of stimuli Is consistent with Evolutionary Advantage view
(and also problematic for perceptual bias accounts)
3. That symmetry preferences occur for familiar faces and are attractive
independent of prototypicality is problematic for the perceptual bias view
4. That symmetry predicts attractive in non-visual stimuli is problematic
for the perceptual bias view and suggests attractiveness of symmetry
reflects an attractive underlying quality

21. Next week: Does facial attractiveness signal health
Many theories of attraction (e.g. evolutionary advantage
view) propose that facial attractiveness signals health
Next week we’ll review the evidence for this claim.