Facial expressions run in the family

Do you look like your father when you're angry? Probably more than you'd imagined. Facial expressions may be inherited, Israeli researchers say.

According to scientists, every person has a set of facial expressions that is unique to them, a signature of their identity that remains stable over time. Stable patterns of facial expressions arise before a baby is six months old, but until now, scientists were unsure whether these patterns were learned or innate.

"We were interested to examine whether there is a unique family facial expression signature," said lead author Gili Peleg from the University of Hafa in Israel. "We [correctly] assumed that we would find similarities between the facial expressions of relatives."

The study, which is published today in the U.S. journal, Proceedings of the National Academy of Sciences, involved 21 participants who had been blind from birth, each with either one or two relatives who had normal vision. According to the researchers, blind individuals have no way of learning the facial expressions of their relatives by mimicry. The common perception that blind people touch other's faces to sense their expressions was revealed to be, in fact, very impolite behaviour.

The scientists induced six emotional states in each individual - sadness, anger, joy, think-concentrate, disgust and surprise - and then documented all the facial movements the person made while experiencing a particular emotion.

Forty-three different facial movements were recorded, including movements such as: biting the lower lip on the left-hand side; moving the lips while pressed together, as though chewing; rolling the upper lip inside the mouth; sticking out the tongue slightly while touching both lips; and pulling down the corners of the mouth while pushing the chin forward.

A computer program was used to allocate the blind individual to a family according to the types of movements observed and their frequencies. The blind individual was allocated to the correct family 80 per cent of the time when using information from all six emotional states.

"These findings indicate the existence of a hereditary basis for facial expressions," Peleg explained.

When each emotional state was analysed separately, the computer correctly allocated the blind individual to his or her family most often for the negative emotion anger, at 75 per cent.

"Negative emotions increase the frequency and diversity of facial movements. The chance to find similar movements raises in a situation in which more facial movements are displayed," according to Peleg.

To induce a state of anger, the researchers asked each person to relate a past experience which caused them to feel angry. The individuals were encouraged to use as much detail as possible in order to relive the experience. This was also how sadness and joy were induced.

Think-concentrate is an "intellectual emotion" first described by Charles Darwin in 1872. This emotional state was evoked by asking individuals to solve a few puzzles of increasing difficulty. While they were concentrating on a puzzle, surprise was induced by suddenly asking the individual a question in gibberish. To induce disgust, they were told a story that included "disgusting" details.

This study paves the way for discovery of the genes that influence facial expressions. According to the researchers, "Genes may control muscles' and bones' structure, innervation and even perception." Further research will explore the evolutionary significance of these heritable facial expressions.

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