• Question from:Gideon

I understand that this question cannot entirely be answered by biology as there may be equal parts neurology and social-psychology, among other considerations, necessitated to reach a larger conclusion; however, I am curious as to whether or not human facial symmetry is increasing over time and if so is there an equation that describes that correlation?

For that matter,  if subconscious recognition of facial symmetry as a indicator of a potential mate's health is common in humans, is the same true for other mammalian species?  If so, can we expect facial symmetry to increase over time in most, if not all, mammalian species?

How much of facial symmetry is do to genetics versus "hickups" in embryonic / fetal development?  If this is the case then we would not see an increase in facial symmetry because the decreased likelihood of offspring for individuals with less facial symmetry would not affect the gene pool for that trait?

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  • Barts and the London, London
  • Posts: 268

Your arguments in favour of increasing facial symmetry are evolutionarily sound. However, evolution takes place over very long periods of time and so even if it is true it may not be measurable for a very long time. I don't know if any studies have been done but others on here may do.

Subconscious recognition of facial symmetry is an indicator of a potential mate's health in other mammals as well.

Wiki has a good article on facial symmetry in humans:

http://en.wikipedia.org/wiki/Facial_symmetry

Do post again if you have further questions.

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  • University of Bristol
  • Posts: 2,463

Playing devil's advocate I question how good the evidence is that facial symmetry and genetic health are linked. As Reetika says if it occurred in animals (and accepted truth is that it does) then by now we should be seeing many mammals that are largely or completely symmetrical - is that the case?

Further why would facial symmetry be expected to be related to health. Yes the opposite is true ie highly asymmetric facial features are often caused by genetic abnormalities but is the converse true with the bounds of "normal" Gaussian variation?

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  • Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
  • Posts: 237

I don't have an actual citation for this, but I remember being told as an undergraduate (probably in my animal behaviour class) that there was a point beyond which increasing asymmetry actually seemed to have a detrimental effect on attractiveness. That is, study participants tended to score perfectly or near-perfectly symmetrical faces as less attractive than ones that were just slightly asymmetrical. If that's true, there might be an optimum level of facial symmetry, from the point of view of sexual selection, that is characteristic of normal, healthy humans and falls a bit short of perfect symmetry.

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  • Brown University/Royal Veterinary College
  • Posts: 323

There is actually a wikipedia article on this, but states itself that current research is not referred to:

http://en.wikipedia.org/wiki/Facial_symmetry


What is of interest there is that it lists a number of health issues related to facial asymmetry.


However, it's not surprising that symmetry should be seen as attractive, or at the very least, not abnormal, given that we are bilatterally symmetrical animals.

Which kind of counter's David's point that we should be seeing symmetrical animals: generally we are.  That's maybe a bit flippant, and obviously not addressing the point that animals should become more symmetrical through time, but then how much more symmetrical can a population become?

Corwin, if you can find a refference that slightly asummetrical faces are more attractive I'd love to see it - I'd find it quite surprising.

Note that 'Britain's most beautiful face' (http://www.whatsontianjin.com/news_imag … gate_1.jpg) is pretty darn symmetrical.

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  • University of Bristol
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I think my question was unclear:

I accept there is very good evidence in humans and other species that facial symmetry = attractiveness. My question is what evidence is there that symmetry is a measure of genetic health/fitness?

The converse is clearly true: very asymetric faces are usually caused by mutations in genes important for development. BUT that does not mean that normal minor variations in symmetry make a person less "fit" than someone with almost perfect symmetry.

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  • Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
  • Posts: 237

Peter:

I don't have time for anything like a proper literature search, but this paper by Rhodes et al. (although a bit dated) addresses the issue fairly extensively.

http://www.springerlink.com/content/eq4178xr00474432/

Basically, Rhodes et al. found that symmetry was correlated with perceived attractiveness, and that the effect persisted right up to the point of (artificially generated) perfect symmetry. However, they cited a couple of previous studies that had indeed found perfect symmetry to be less attractive than slight asymmetry, and those were presumably the ones my animal behaviour professor was talking about. Rhodes et al. suggested that the specific way the perfectly symmetric faces were created in the other studies (by mirroring one half of a normal face) might have introduced features that made them less attractive.

David:

The Rhodes et al. paper contains some discussion of the evolutionary issue too, although it doesn't really address your question of whether there's good evidence that small differences in symmetry correlate with small differences in fitness. Even if they don't, however, it's possible to imagine (as I may have argued on here before) that evolution's way of encouraging avoidance of very asymmetric potential mates was to favour the appearance of a simple "symmetry good!" rule that was never fine-tuned to the point of ceasing to operate within the non-pathological range of symmetry.

  • University of Bristol
  • Posts: 350

Is the perception of what an observer considers attractive re. facial symmetry influenced by the symmetry of the observer's own face (almost symmetrical may be  'symmetrical enough' as Corwin relates above)?