Anthony Little

Symmetry in Animals

Preferences for
Symmetry

Non-Human Species Preferences for Symmetry
• Scorpion fly females prefer males with symmetrical bodies
Thornhill, 1992
• “All animals prefer symmetry in their mates. The male Japanese scorpion flies with the most symmetrical wings gets the most mates."
Gil Grissom, CSI, Season 2

Non-Human Species Preferences for
Symmetry
• Female barn swallows prefer males with symmetrical tail feathers
Møller, 1994, Anim Behav
• Female zebra finches prefer symmetrical males
Swaddle & Cuthill, 1994, Nature

Symmetry
• Most features are supposed to be symmetrical
• Deviation from symmetry reflects imperfect development
• Symmetry = a measure of quality

Measuring
Symmetry
Attractiveness ratings of women correlate with measured symmetry
Grammer & Thornhill, 1994, JCP
Penton-Voak et al., 2001, PRSB

Symmetry Manipulation
The lower images are made using the left/right average of the 224 feature points
(only 4 are
Marked here)

Original
Symmetric
Symmetry is found attractive…
Perrett et al., 1999, EHB

Symmetry is More Associated with
Attractiveness in Opposite-Sex Faces
Little et al., 2008, Behavioural Ecology

The Hadza of Tanzania
• Live in small bands
• Hunt with bows and arrows
• Gather roots, tubers and wild fruits
• Conditions representative of human evolution?

Hadza Face Preferences Symmetry
5 pairs original symmetric

Hadza Face Preferences Symmetry
5 pairs original symmetric

Little, Apicella, & Marlowe (2007) Proc Royal Soc

Macaque Preferences Symmetry
Preferred by females asym
• Gaze longer at symmetrical face
Waitt & Little (2006) IJP sym

Relationships between
Sexual Dimorphism and
Symmetry

Measuring
Symmetry &
Sexual dimorphism
Penton-Voak, et al. 2001,
Proc Royal Soc

Hadza, Europeans, & Macaques
 Measured symmetry and masculinity in:
 70 Hadza, 177 European, 123 Macaques
 Males

Hadza, Europeans, & Macaques
 Correlation between S and M in all
 Suggests common origin to development
 Good-genes? Good environment?

Conclusions
• We can examine the importance of certain traits across species:
• Many animals ‘prefer’ symmetric mates
• Facial asymmetry appears linked to other important traits in primates

Conclusions
• There are some broad similarities between humans and other animals…
• Understanding how other animals choose their mates can help us understand behaviour in humans
• ...and vice versa