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Revision lecture 2007. Exam formant. Three questions in Section A Three questions in Section B You must complete one question from each section. Revision lecture outline. Attractiveness & health Self-resemblance as a cue of kinship Why are symmetric faces attractive?

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exam formant

Exam formant

Three questions in Section A

Three questions in Section B

You must complete one question from each section

revision lecture outline

Revision lecture outline

Attractiveness & health

Self-resemblance as a cue of kinship

Why are symmetric faces attractive?

Averageness & attractiveness

1 attractiveness health

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 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 health5

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 measure

1 attractiveness fertility

1. Attractiveness & fertility

Law Smith et al. 2006

High levels of oestrogen and progesterone are associated with fertility among women and are positively related to women’s facial attractiveness

Penton-Voak et al. 2003

Low 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 fertility7

1. Attractiveness & fertility

Roberts et al. 2004

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

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

1 attractiveness good genes

1. Attractiveness & ‘good genes’

Roberts et al. 2005

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

1 attractiveness health9

1. Attractiveness & health


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

2. Self-resemblance as a cue of kinship

Two 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 account is ‘mere exposure’ - self-resembling faces are familiar and therefore attractive]

2 self resemblance as a cue of kinship11

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 kinship12

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 kinship13

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 kinship14

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 kinship15

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 kinship16

2. Self-resemblance as a cue of kinship


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 (I.e. hard to explain in terms of ‘mere exposure’ effects)

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


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?

evidence for perceptual bias
Evidence for Perceptual Bias

Symmetry preferences seen in:

  • objects
  • decorative art

Rensch, 1963

Gombrich, 1984



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



neural networks perceptual bias
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)


prototypes and perceptual bias
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


Prototypes and Perceptual Bias


  • 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

perceptual bias accounts cannot accommodate individual differences in symmetry preferences
Perceptual bias accounts cannot accommodate individual differences in symmetry preferences


women like symmetric male faces more than relatively unattractive women do

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

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
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 attractive independent of prototypicality (Rhodes et al)

Also - symmetry predicts attractiveness in other modalities


There is evidence perceptual bias can cause symmetry preferences


Perceptual bias accounts cannot explain human’s symmetry preferences


4. Averageness & attractiveness

The more faces that contribute to an average face (i.e. the more average it becomes), the more attractive it is judged

3 face



10 face



Langlois & Roggman, 1990


Biological basis

That babies and adults prefer average

faces suggests that averageness

preferences have a biological basis - DeHaan et al

Cross-cultural preferences also reported (Rhodes et al)


Are averageness preferences artefacts?

Average faces tend towards high symmetry - the

attractiveness of average faces may reflect preferences

for symmetry

Valentine et al. (2004) investigated if increasing

the averageness of profile face views

increased their attractiveness

(i.e. increased averageness independent of symmetry)

Increasing averageness of profiles DID increase

attractiveness (even though no change in symmetry)

Increasing averageness of shape alone also sufficient to

increase attractiveness (e.g. Little & Hancock; Rhodes et al)


2. Evolutionary advantage view of averageness preferences

Thornhill & Gangestad (1993) noted that genetic

heterozygosity may cause an average appearance and

is conducive with good health

Average faces may be attractive because they

signal health

Consistent with this, Rhodes et al. (2001) found that

women with average faces had fewer past health

problems than those with distinctive faces


3. Perceptual bias view of averageness preferences

Average faces may be preferred as a by-product of the

visual system

Average faces are (by definition) prototypical and will

therefore be very similar to mental representations

used to process faces

This similarity to mental prototypes will cause

unfamiliar average faces to be perceived as familiar


Evidence against averageness accounts of attraction

Perrett et al (1994) showed that very attractive faces

are not average

Average of 60

Average of

Most attractive


Least attractive Most attractive

Most average Least average


Averageness hypothesis suggests averageness is the critical determinant of facial attractiveness

Average faces are attractive, and this can’t be explained by blemish-free skin or symmetry preferences

Average faces are attractive to diverse ages and people from diverse cultures

Perceptual bias and evolutionary advantage accounts of averageness preferences have been advanced

Perrett et al. (1994) showed that attractive faces deviate systematically from an average appearance