January 10, 2013

Eye color, face shape and perception of trustworthiness

An old popular Galician song said:
Ollos verdes son traidores...
azules son mentireiros,
os negros e acastañados son firmes e verdadeiros.

Translated:
Green eyes are treacherous...
blue ones are deceitful,
the black and brown ones are loyal and truthful.

Just word of a silly mariner song? Intriguingly science confirms now, in a way, part of this perception (at least for blue and brown eyes).

But notice please that it is the precisely the perception what is being confirmed: people seem to perceive blue eyes in general as somewhat less trustworthy. The study says nothing about people with blue eyes being untrustworthy in fact, just that we tend to distrust them more than people with brown eyes.

Karel Kleisner et al., Trustworthy-Looking Face Meets Brown Eyes. PLoS ONE 2013. Open access → LINK [doi:10.1371/journal.pone.0053285]

Abstract

We tested whether eye color influences perception of trustworthiness. Facial photographs of 40 female and 40 male students were rated for perceived trustworthiness. Eye color had a significant effect, the brown-eyed faces being perceived as more trustworthy than the blue-eyed ones. Geometric morphometrics, however, revealed significant correlations between eye color and face shape. Thus, face shape likewise had a significant effect on perceived trustworthiness but only for male faces, the effect for female faces not being significant. To determine whether perception of trustworthiness was being influenced primarily by eye color or by face shape, we recolored the eyes on the same male facial photos and repeated the test procedure. Eye color now had no effect on perceived trustworthiness. We concluded that although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes.

So the authors conclude that it is not eye color but associated face shape what drives untrustworthiness because the phenotype associated with blue eyes is more angular, less rounded, at least for males:

Figure 2. Shape changes associated with eye color and perceived trustworthiness.
Thin-plate spline visualizations of the way face shape correlates with eye color (a–f) and trustworthiness (g–i). Generated face shapes of blue-eyed woman (a) and brown-eyed woman (c) compared to average female face (b). Generated face shapes of blue-eyed man (d) and brown-eyed man (f) compared to average male face (e). Generated face shapes of untrustworthy-looking man (g) and trustworthy-looking (i) man compared to average male face (h). The TPS grids of perceived trustworthiness for women are not shown because shape analysis did not meet statistical significance. The generated facial images (a–f) were magnified 3x for better readability.

They claim that they found no correlation with facial shape for women but I find in the image above almost exactly the same pattern for men and women and not only what they detected: notably the blue eyed people (both genders) and the less trusted men all have in my opinion:
  • Smaller eyes
  • More serious (defiant, analytic, unsympathetic) expression
  • Proportionally broader face or at least jaws
In general the faces to the left look significantly colder, less empathic, a perception that blue eyes can only enhance.

The authors ponder if there is a phenotype linkage disequilibrium associating face and eye color, what seems plausible. But then go on speculating about sexual selection and what not. 

In this sense Razib has an interesting critical analysis questioning if selection is behind the blue eye incomplete sweep in West Eurasia or Europe. If I understand him correctly he seems to suggest, never clearly naming it, that blue eye may have been favored because of the associated skin pigmentation trait, a key adaptive value in the dark winters of Europe and very especially the northern half of it.


Update: is this a peculiarity of Central Europe or the Czech Republic?

A reader sent me an email in which it was questioned if this association is peculiar of the Czech Republic, where the study was performed, and can't be extended for example to Britain. Examples of soft-faced blue-eyed Britons mentioned were Hugh Grant and Alec Baldwin (I'm not sure if Baldwin is such a good counter-example but Grant is for sure one such case). 

I find it a very good criticism and hope that entices debate.



See also: Causes of skin and hair color variance in Europeans remain undetermined.

8 comments:

  1. It's interesting but i wonder if it might be a regional bias from a historical border zone?

    ReplyDelete
  2. Actually now i think of it i wonder if it could be anything to do with pupil dilation i.e. it's easier to see if blue-eyed people *don't* have dilated pupils.

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    Replies
    1. People were presented with photos and then also with photos with recolored eyes. The latter did not entice any color associated response but retained the pre-colored eyes one, suggesting that the reason is not the eyes but face shape commonly associated to blue/brown eyes - because of linked desequilibrium in genetic inheritance: 95% of blue eyes come after all from a unique ancestor and other aspects of the phenotype are probably inherited with them in the same package, maybe not always but often enough.

      AFAIK the authors did not test for hair or skin shade, which should be associated to blue eye color to some extent. Is possible that paler shades are influential in this.

      Whatever the case I find it most intriguing.

      Delete
    2. "Whatever the case I find it most intriguing."

      Yes, very.

      Delete
  3. I find blue eyes most reassuring, but my mother was blue eyed, so I would have imprinted on that color. If I were to redo the study, I would separate the respondents based on their own eye color, and the eye colors of each of their parents. My guess is that personal eye color would have no effect, as we are hardly aware of our own eye color. However, I would not be surprised if there is a detectable bias in favor of maternal eye color.

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    Replies
    1. If you read the study, that was done, and a very small bias was detected only among brown eyed women (but it did not explain most of the results). Blue and brown eyed people responded essentially the same. However, when the eye color was carefully photoshopped, the pattern persisted but not towards apparent blue eyes but towards real blue eyes not visible anymore. That's why the authors considered the face shape pattern as a more likely cause, at least for males (although there might be other reasons as skin tone or hair color which AFAIK were not tested for).

      Also, as I mentioned in the update, the study was done in the Czech Republic and may reflect local peculiarities. It'd be interesting to do similar tests in other ethnic contexts like Britain, Russia or Italy for contrast.

      Delete
    2. Yes, it would be very interesting to see this test done in other countries.

      A popular Lithuanian adage goes: "rudos akys apgaulingos" (=brown eyes are treacherous). An old song:
      "Žalios akys apgaulingos,
      rudų akių nemyliu,
      o be mėlynų akelių
      aš gyventi negaliu"

      Translation:
      Green eyes are treacherous,
      brown eyes I don't love,
      but without the blue eyes I cannot live.

      Delete
    3. I see that this obsession of singers for classifying people (well, mostly women) by eye color is cosmopolitan. :D

      Delete

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