PS4029/30

Perspectives on social attributions

Lecture 4

1. Accounts of sym preferences (recap)

2. Does symmetry signal mate quality?

3. Is symmetry particularly attractive in mate choice relevant stimuli?

4. Is symmetry attractive independent of prototypicality?

5. Symmetric individuals are not only visually attractive

Lecture 3: Evolutionary advantage accounts of symmetry preferences

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

1. Evolutionary advantage view

Symmetry is attractive because of advantages associated with

choosing a symmetric mate

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

Swaddle & Cuthill, 1994, Nature

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 somepositive relationships reported between symmetry and ‘matequality’

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

Manning et al., 1998, Evo Human Behav

Gomendio et al., 2000, Proc Royal Soc

Møller et al., 1995, Ethol. Sociobio

Lagesen & Folstad, 1998, Behav Ecol Sociobio

Symmetry and Quality IIHumans

– 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]

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

The Mona Lisa

The Thatcher Illusion

Eyes and mouth inverted

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

Symmetry Preference in Upright and Inverted Opposite-Sex Faces

Little & Jones, 2003, Proc Royal Soc

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

Symmetry in Familiar Faces

• Even though symmetric version is less familiar (and less prototypical), symmetry is still preferred - Little and Jones, 2003)

Symmetric Asymmetric

Symmetry and prototypicality

• Symmetry attractive independent of averageness

(Rhodes et al., 1999)

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

Ratings of the attractiveness of faces and symmetry are +vely correlated when effects of distinctiveness are controlled usinga partial correlation design

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)

Prototype faces tend towards very high symmetryComposites 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)

Composite of asymmetric faces

Composite of symmetric faces

Judged:

AttractiveHealthyFit

Judged:

UnattractiveUnhealthy

Unfit

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)

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 thanOther 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 symmetryreflects an attractive underlying quality

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.