We recognize siblings based solely on facial similarity

This is a guest post by Christy Tucker, one of Greta's top student writers from Spring of 2007.

i-eca0cf2af9fc3ac4445c7dff7d8aab70-research.gifTake a look at the following paintings. How alike are they? How can you tell--which clues help you determine similarity? Now, which of these girls are related? If only two of these young girls are related, how would you determine which two? Would they be the same ones that you thought looked very similar?


Laurence Maloney and Maria Dal Martello studied observer's ratings of the similarity between two children's faces in relation to judgments on whether the two are siblings. Do we simply note similarity when trying to figure out siblings? Or do we use a different process? Pairs of pictures of children with neutral facial expressions like the one below were shown to two groups of observers.


The first group of viewers rated how similar on the scale of 1 (not similar) to 10 (similar) the children appeared. They were not told that the pairs of children could be siblings. The second group of viewers viewed the same picture sets, and then answered whether the children were siblings or non-siblings. This time, the observers were told that half the pairs were siblings.

Maloney and Dal Martello found that children who were rated to be more similar were more often judged to be siblings, as demonstrated by the graph below.


Consistent with this result, when a pair was not believed to be similar, they were rarely classified as siblings. Subsequent statistical analysis revealed that viewers did not take into account gender or age when determining similarity. In addition, the straight upward-sloping line in the graph suggests that similarity ratings are based on some sort of built-in formula.

A later study by Maloney and Dal Martello addresses the specific features of the face on which observers focus during their assessment of similarity or relatedness. They conclude the characteristics of the upper face are used to make projections about relatedness of children, since the lower face is not fully developed until early adulthood. Take a look back at the paintings of the four girls. The girls are actually all sisters, taken from Thomas Gainsborough's 1787 The Marsham Children. The ratio of upper face size to lower face size generally indicates age. Does that help you determine the relative age of the sisters? Would observers spotlight the lower face to decide whether adults are related, since the structure of their lower faces are already fully formed? It is truly fascinating to realize that when we talk by a group of people, our minds are engaging in a process of similarity and relatedness assessments that affect our judgments of them and interactions with them!

Maloney, Laurence T. & Maria F. Dal Martello (2006). Kin recognition and the perceived facial similarity of children. Journal of Vision, 6, 1047-1056.

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As a child I was severely nearsighted. At arms' length, my own fingers were blurry. I could not see faces clearly unless they were so close they were too close to focus. It was not until 10 that I got glasses, which opened up a whole new world to me. For the first time I learned what people actually looked like to other people. I also noticed street signs for the first time, I saw stars in the night sky, and I saw my own face in a mirror.

All my adult life, I've had no idea what my own face looks like. I can find myself in a group photo by eliminating the ones I know. I don't recognize my face in the mirror; I don't see it as a face, just parts of the front of my head.

I have always failed at seeing family resemblances (except for identical twins). I think there may be ordinary experiences children have early in life that help them develop the ability to see family resemblances. The cutoff age might be 10, or it might be much earlier.

By Once Near Blind (not verified) on 09 Jul 2007 #permalink

My younger sister and I are 4 years apart and I swear to God that if we were of the same height, a lot more people will mistake us than there already are! :)

Our teachers mixed us up. Our friends kept reminding us how we looked like we were photocopied, or made from the same mould. Even our boyfriends said we look alike!

My brother and I are often thought to be of different nationalities, based on how we look (although a few people do find us similar).

By valhar2000 (not verified) on 10 Jul 2007 #permalink

What happened to "once near blind" also happened to me, although I may have had less of a challenge adjusting because I got glasses three years earlier. I still remember the amazement of discovering streets and businesses were labeled - I thought adults just memorized them all.

Anyway, I recognize people now (not well), but have problems visualizing faces. This is annoying because I'm an artist. Although I can paint photorealistic portraits of imaginary people, I could not portray my own mother accurately without a photo for reference! It's not a matter of technical skill, but of some sort of mental pathway for differentiating details - perhaps the type described in this post.

I am best at recognizing people by the way they walk - a skill I had to develop as a child when visiting a crowded public park or pool, surrounded by large moving blurs. But in a less technical age, I'd have been weeded out by natural selection long ago.