Why your face stands out from the crowd

Human faces are much more diverse and varied than we would expect, compared to animal visages and other body parts.
23 September 2014

Interview with 

Michael Sheehan, University of California


Take a long, hard look in the mirror. Unless you are an identical twin your face is one of a kind, which is the main way your friends and family can recognise you. But why do humans have such variation across faces compared to other animals? Michael Sheehan looked at US army data to discover whether our faces really are so different...

Michael -   One of the things that I think is really striking about humans is, as we look around at people, we notice that they're all really variable.  We use that variation to tell each other apart and to recognise who's who in our social interactions.  It's particularly interesting especially when you compare humans to other animals that you see as you walk around that we seem strikingly much more variable than a lot of the species we see.  We also have really complex social interactions which suggests that given that we use the variation for recognition that maybe there's something about our social interactions that may have sort of driven our morphology to be much more recognisable.  And so, we're interested in looking to see whether there was any evidence that our social interactions and being recognisable may have shaped our faces over evolutionary time.  What's really quite striking as well is that our faces are very variable but the rest of our bodies aren't necessarily as strikingly variable necessarily.  We used a US army database for they measured lots of different - both facial and the rest of the body - morphology of service members with a wide range of ages and ethnicities.   When we do that for both men and women in all cases we examined faces were variable both in the sense that the traits in the face turned higher levels of variability, but also I think quite strikingly, the traits in the face are less correlated with each other.  So essentially, what that means is that even though tall people have long arms and long legs, and sort of all the parts of their body are generally bigger, they don't necessarily have bigger facial traits.  And so, it's not the case that individuals with large noses necessarily have widely spaced eyes.  The fact that you can mix and match different sizes of facial traits together, it's a huge range of combinatorial variation that ends up making people very unique looking.

Georgia -   Why is there so much variation across our faces and not amongst our other body parts?

Michael -   So the hypothesis we were working with is that in the case of humans, we use faces as one of the main things we use to recognise individuals.  So, I think from anyone's own experience in life, you know that being able to recognise who you're interacting with is really important.  And so, the idea in this case that we're arguing is that there may have been some selection on facial traits to be more recognisable, given that that is the trait that we happen to use for recognition.

Georgia -   So, how does having a recognisable face actually help you?

Michael -   The really basic idea is that in many situations, it can be costly to be confused with other individuals.  It could be that you get some aggression or punishment that's actually meant for someone else.  But because you look like them, it ends up going to you.  The other reason that it could be costly to be confused with other individuals is that if you did something really great, you want to get all the rewards or the benefits of doing that, then if someone else looks like you, they may in fact get whatever prize or reward that you may have gotten.  In an evolutionary sense, you can imagine that if you're sort of the hot shot, that maybe there is - you're going to get some resource that someone else wouldn't get or a mating or something like that, you could potentially lose out on if there's confusion about who actually did the great deed.


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