Like father, like son

If you've ever noticed that kids have the same facial expressions as their parents, you're not alone. The usual explanation for this similarity is learning -- kids watch their parents' facial expressions and then take them on themselves. This seems like a natural hypothesis considering another well-worn observation: that couples tend to resemble each other more and more over time. What more rational basis for this resemblance than subconsciously adopting each others' facial expressions?

But so far, we're really in "old wives' tale" territory. There is another hypothesis for similarity between parents and kids -- that their genes make them look similar. Peleg and colleagues (2006) have examined facial expressions in families to test whether genes underlie the variation to an observable extent.

The really interesting part is that they test a sample of blind subjects for similarities in facial expressions with their relatives.

Here's the abstract:

Although facial expressions of emotion are universal, individual differences create a facial expression "signature" for each person; but, is there a unique family facial expression signature? Only a few family studies on the heredity of facial expressions have been performed, none of which compared the gestalt of movements in various emotional states; they compared only a few movements in one or two emotional states. No studies, to our knowledge, have compared movements of congenitally blind subjects with their relatives to our knowledge. Using two types of analyses, we show a correlation between movements of congenitally blind subjects with those of their relatives in think-concentrate, sadness, anger, disgust, joy, and surprise and provide evidence for a unique family facial expression signature. In the analysis "in-out family test," a particular movement was compared each time across subjects. Results show that the frequency of occurrence of a movement of a congenitally blind subject in his family is significantly higher than that outside of his family in think-concentrate, sadness, and anger. In the analysis "the classification test," in which congenitally blind subjects were classified to their families according to the gestalt of movements, results show 80% correct classification over the entire interview and 75% in anger. Analysis of the movements' frequencies in anger revealed a correlation between the movements' frequencies of congenitally blind individuals and those of their relatives. This study anticipates discovering genes that influence facial expressions, understanding their evolutionary significance, and elucidating repair mechanisms for syndromes lacking facial expression, such as autism.

Turns out that Darwin had the idea first:

About 130 years ago, Darwin mentioned facial expressions in blind-from-birth individuals in the context of heritability: "The inheritance of most of our expressive actions explains the fact that those born blind display them, as I hear from the Rev. R. H. Blair, equally well with those gifted with eyesight" (Peleg et al. 2006:15922).

Still, the study is incomplete -- it has a small sample of subjects, and doesn't have the data to try to estimate the heritability of these expressions. Indeed, as "gestalts," the expressions themselves are statistically difficult to work with.

And speaking of facial expressions -- tonight's "Dancing with the Stars" show featured a body language expert examining how each of the competitors responds subconsciously to being judged. Mario Lopez takes a submissive posture when he is about to hear what the judges say, while Joey Lawrence licks his lips compulsively out of nervousness. They'd better stay out of poker games!

References:

Peleg G, Katzir G, Peleg O, Kamara M, Brodsky L, Hel-Or H, Keren D, Nevo E. 2006. Hereditary family signature of facial expression. Proc Nat Acad Sci USA 103:15921-15926. DOI link