In his 1872 book The Expression of Emotion in Man and Animals, Charles Darwin related an interesting case described to him by his cousin, twin researcher Sir Francis Galton: A man had a habit of raising his right arm while asleep and letting his wrist fall heavily on the bridge of his nose. Years after the man's death, his son was found to do the same.
Like this account, most reports of gestures or facial expressions shared by family members are anecdotal. But researchers in Israel have done a study showing that families have characteristic facial expressions, ones even shared by blind members of the families. The results suggests that such expressions may be inherited and thus under some genetic control.
Evolutionary biologist Eviatar Nevo of the University of Haifa at Oranim and his graduate student Gili Peleg studied 21 congenitally blind people from different families, as well as 1 or 2 sighted relatives of each. Through techniques such as asking subjects to relate personal experiences, the researchers provoked a repertoire of 43 facial gestures that they said covered six emotional states: sadness, anger, disgust, joy, surprise, and concentration.
To gauge family similarity, the researchers carried out an exercise that Nevo compares to finding the strongest individual in two rope-pull teams. The team had computers analyze an individual blind person's facial expressions and compare them to those of two groups of 10 families each: one containing the family members and one without. If facial expressions do not run in families, the researchers expected the computers to assign individual subjects to the correct group 50% of the time. But the researchers found that the subjects were matched with the correct group 80% of the time.
The team, which reports the study online this week in the Proceedings of the National Academy of Sciences, concludes that there is such a thing as a "family facial expression signature." The correct classifications were highest for people showing anger, says Peleg, indicating a particularly high heritability for this expression. In contrast, the researchers found less family resemblance for joy and sadness--possibly because expression of these emotions is more uniform across groups.
The study is "a very creative attempt to get at the genetic underpinnings of facial expressivity," says psychologist Nancy Segal, a twin researcher at California State University in Fullerton. She adds that the work "opens up new avenues for research" that could set more precise heritabilities and perhaps cast light on evolutionary reasons for why relatives have similar facial expressions.