Symmetry Is Sexy: Reply to Hodgson's 'Symmetry and Humans'
Burriss, Robert P., Antiquity
In his contribution to the Antiquity debate over the viability of Kohn and Mithen's 'Sexy Handaxe Theory' (1999), Hodgson (2009: 195-8) asserts that 'symmetry is not connected with health and thus cannot have served as a sign of genetic worth'. Because I find his interpretation of the current literature on symmetry and its relationship to health and attractiveness to be flawed, I cannot accept Hodgson's argument. I address each of my concerns below in the first part of this response. I also remain unconvinced that, even if Hodgson's assertion were supported by the literature, it would necessarily follow that symmetry in manufactured objects, including Acheulean handaxes, cannot signal 'sexiness'. In the second part of my response I explain why I consider this to be so.
Symmetry, attractiveness and health
Developmental stressors, such as pathogenic infection, genetic homozygosity and environmental trauma, can result in deviations from perfect bilateral symmetry that are known as fluctuating asymmetries (Mealey et al. 1999). A person's symmetry may therefore honestly advertise their phenotypic health and genotypic quality, and this information may prove useful in a mate selection context (Grammer & Thornhill 1994). Although the link between fluctuating asymmetry (FA) and health remains controversial, there is a good deal of support for symmetry as a measure of quality. As Hodgson correctly states, several authors have demonstrated that facial FA is negatively correlated with perceived health in humans (Grammer & Thornhill 1994; Noor & Evans 2003; Fink et al. 2006). It is true that Rhodes et al. (2001b) did not show a link between FA and actual health, but their participants were young (17 years) and it is possible that the effects of certain developmental stressors do not manifest themselves fully until adulthood (Wilson & Manning 1996). It is well established that body FA is positively associated with the incidence of health problems, such as low back pain and a number of genetic disorders (Thornhill & Moller 1997; Waynforth 1998; Milne et al. 2003; Al-Eisa et al. 2004), as well as with measures of psychological, emotional and physiological stress (Shackelford & Larsen 1997), and is negatively related to IQ (Furlow et al. 1997). What's more, persons with less symmetrical faces and bodies tend to experience longer and more frequent respiratory infections (Thornhill & Gangestad 2006) and, in chimpanzees, facial FA is negatively associated with zookeeper assessments of physical and mental health (Sefcek & King 2007). Though I would agree with Hodgson that the link between facial (rather than body) FA and real (as opposed to perceived) health remains equivocal, on the whole I am unconvinced by his argument that symmetry is unlikely to be connected with health.
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Hodgson makes the further assertion that facial symmetry may not be attractive. Here he is on discernibly shakier ground. Older studies that have demonstrated a preference for asymmetry (e.g. Langlois et al. 1994; Kowner 1996; Mealey et al. 1999) used chimaeric ('mirrored') faces. Chimaerae are now agreed to represent a suboptimal method of asymmetry manipulation. Figure 1 shows an unaltered facial photograph (a) and two chimaeric images made from the left (c) and right (d) sides of the face, demonstrating that this method produces abnormalities in shape and pigmentation. These abnormalities become more pronounced as the asymmetry of the original face increases. This is because facial features, such as the nose or mouth that are positioned asymmetrically with reference to the facial midline, cannot be satisfactorily bisected. It is therefore unsurprising that in these earlier studies asymmetry was preferred over symmetry. More recently, authors have used sophisticated computer graphics techniques to manipulate facial asymmetry, warping an image's RGB information to fit a symmetrically remapped shape (see Figure lb). …