The sexiness of facial symmetry across cultures and species

There’s a new PLoS ONE paper making the rounds in the press today. The research behind it fits the kinda stuff you may see on Dienekes’ Anthropology Blog and sometimes on GNXP… it is basically an investigation on the attractiveness of a symmetrical face. The paper is published open access, under the title, “Symmetry Is Related to Sexual Dimorphism in Faces: Data Across Culture and Species.” It comes from psychologists and anthropologists in the U.K. and the U.S.

This subject is extremely interesting. The face has many functions in social behavior — moods are assessed from emotions expressed on the face. The face also functions as a billboard, advertising the quality of the mate. More attractive faces are often thought to be higher quality mates. Both symmetry and degree of sexual dimorphism have been linked to affect the attractiveness of human face shape.

In this study, subjects were given arrays of photos of 500 faces from people of European and African ethnicity as well as photos of non-human primates (macaques). About a third of the faces were male and the rest were females. The subjects were asked to judge for the most attractive face. The most attractive faces were then measured for symmetry. Symmetry was determined by measuring deviations from the midline, as well as measurements for the distance between the eyes. In total 6 measurements were made to assess bilateral symmetry.

The degree of sexual dimorphism was also measured. The distance between specific points, like the prominence of the cheekbone and ratios of the height of the jaw to the lower face height, lower face height to the face height and ratio of the width of the face to the height of the lower face were made. In all samples, symmetric males were ones who also had more masculine facial proportions and symmetric females had more feminine facial proportions. I’ve put up a figure that shows the highs and lows of attractive faces form their study.

These conclusions further validate the notion that sexual dimorphism and symmetry in faces advertise mate quality. I kinda have an issue with how the authors are phrasing their results — they had two ethnic groups in their study but conclude that symmetry & dimorphism is attractive in all cultures. It is very probably that other cultures also share this sentiment, but it is over-stretching the results to say that this reaction is evident ALL cultures and species based off of two ethnic groups.

I’m also not too sure how the authors justify that sexual dimorphism and symmetry in the face provides evidence that there must be a biological mechanism linking the two traits during development. This could be because I really don’t know much about evolutionary psychology. There is without a doubt something going on psychologically that makes people associate symmetry and dimorphic faces as attractive, how that translates to mate quality is highly debatable. On a related sidenote, I find the data about our ability to find attractive primate faces also very interesting, the authors suggest that,

“the signaling properties of faces are universal across human populations and are potentially phylogenetically old in primates.”

Which indicates that there’s been some sort of selection in the primate lineage that has predisposed us to associate symmetrical, dimorphic faces as attractive.

    Little, A.C., Jones, B.C., Waitt, C., Tiddeman, B.P., Feinberg, D.R., Perrett, D.I., Apicella, C.L., Marlowe, F.W., Reimchen, T. (2008). Symmetry Is Related to Sexual Dimorphism in Faces: Data Across Culture and Species. PLoS ONE, 3(5), e2106. DOI: 10.1371/journal.pone.0002106

12 thoughts on “The sexiness of facial symmetry across cultures and species

  1. It would be interesting to know if there ever has been a study conducted which focused upon the attractiveness of faces whose features have been affected by a deviant genetic makeup.

    To explain my interest in such a study would be to further deepen the investigation of the claim mentioned in the above post:

    “people associate symmetry and dimorphic faces as attractive”

    For, I am sure that there are people carrying genetic defects who have highly symmetric faces, even if I do admit that some severe genetic defects do produce assymmetric faces. Further, I believe that there are people with healthy genes who suffer from assymmetrical facial features. (It may also be a vain claim of mine as the low-ranked white female face very well could be my own.)

    But, to further add to these aspects which would be interesting to see more of, I wonder if there ever has been a study where the test subjects’ attractiveness have been assessed before the study (or perhaps after). It would be interesting because I have a theory about how low-ranking (masculine) female faces and the associated persons psychologically may try to compensate for their own gentic “flaws” and through that deem the unattractive feminine male face more attractive.

  2. I want to think that nature has selected for attraction to mates with symmetrical faces because perhaps that trait is indicative of a symmetrical physique in general…and, though I don’t know if there’s any biological evidence of this, maybe a symmetrical body simply functions better, making the mate more fit for successful reproduction? I found this interesting passage to back up my ideas:
    “While studying the sexual shenanigans of the common Japanese scorpion fly, Thornhill (Randy Thornhill, a behavioural ecologist at the University of New Mexico, Albuquerque) discovered that males with the most symmetrical wings won the most mates. Similar biases were turning up in other animal studies. Anders Møller, now at the University of Copenhagen, found he could ruin male swallows’ chances of finding mates merely by making their tails less symmetric. One by one, the peafowl, zebra finch and earwig revealed a secret passion for symmetry. Even bumblebees came out of the closet, revealing a preference for flowers with even arrays of petals (see New Scientist, Science, 18 March).
    That’s some evidence for mate preference based on symmetry (albeit admittedly far from the hominid line,) but I would be interested to hear more about the biological function of physical symmetry.It seems to make sense to me in an overly simplistic way: I, and probably most people, would rather drive over a bridge that seems symmetrical rather than the opposite…could a similar phenomenon be at work with mate preference, that the symmetrical are simply better suited for survival? The above poster has argued for the fact that someone with a symmetrical face may still harbor undesirable genetic traits; I would like to know the correlation between physical symmetry and genetic “health.” If anyone can point me to a source, I’d love to hear about it.

  3. I love it when psychologists make sweeping generalizations about humans as a species based on assessments by “the usual subjects.” I.e., whomever they’ve been able to drum up in the local area, most probably students with middle class American or European backgrounds. With no controls for ethnic, regional, or class bias, such “tests” are pointless.

  4. Hey Victor,

    Thanks for your comment. I spoke with Razib, one of the main bloggers at Gene Expression, and someone more well read in this research — he’s indicated that there have been other studies done with different ethnicities with similar results, such as the Papuans in the South Pacific and Ache Indians in Brazil. I haven’t bothered to do literature search to validate, but I trust what he’s saying.

    Basically, it seems pretty ubiquitous that people — regardless of their ethnicity, can pick out the hotties and they are most often ones with symmetrical faces.

    Kambiz

    1. Yeah, and it seems ALL the animals living on the present seem to having been able to pick up “the hotties”, as U say.

      U are a medical student, so how come it’s possible U don’t know that the face symmetry is linked genetically with health ?
      Parasites and mother’s wellfare / diseases may easily damage the cephalus (head) development and so change the face symmetry.

      I don’t know how much U go out in the wild / follow nature film docs, but have U ever seen a flat-headed lion, or short-nosed moose ?

      In our domestic animals, facial unsymmetry is occasionally seen, but in the wild, I think never.

  5. Well, I can’t imagine a face more symmetrical than my own. So maybe I need to get “out there” more, head for the nearest dating bar, waddya say?
    (Actually, that would explain . . . ahhh forget it.)

    Anyhow, thanks Kambiz for filling me in on the extent of these studies. I stand corrected. It’s just that there is so much research out there based exclusively on western norms that pretends to represent “humanity” as a whole. It’s good to learn that there’ve been SOME efforts, at least, to broaden the base.

  6. Nature could not select for more symmetrical features because the type of symmetry discussed here — small deviations from perfect symmetry — is not heritable at all. Selection probably wants to increase the frequency of this phenotype, but there is just no genetic variance in the gas tank.

    The must-read edited volume on this topic is Polak, *Developmental Instability*:

    Lots of good discussion on the heritability across all species studied (lots in the case of asymmetry). The 95% confidence interval of heritability always includes 0, and the mean is typically under 1%.

  7. Would it be UN-PC to re-order the the faces with the “white” faces being towards the bottom with the black ones between the white and the monkey? :-)

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