They might look sleepy, bored and switched off, but people with a tendency to yawn a lot actually do so because they are highly attuned to the social world around them.

Those who are prone to contagious yawning — the mysterious phenomenon by which the urge to yawn can be “caught” by watching others doing it — also have particularly high empathy for the emotions of others, research has suggested. They notice that others are yawning and then unconsciously mirror their actions.

While almost all animals with a backbone yawn, the reflex is only infectious among humans, chimpanzees and some monkeys, and contagious yawning is thought to have evolved as a means of social communication.

A study led by Catriona Morrison, of the University of Leeds, has indicated that infectious yawning is strongly linked to empathy. She found that people who are good empathisers yawn contagiously about three times as often as people with less pronounced social skills. The results, presented at the festival, suggest that the phenomenon has a clear social function. “This is something that is highly evolved, but is not under conscious control,” Dr Morrison said.

Research led by Simon Baron-Cohen, of the University of Cambridge, has indicated that people who are good at systemising, or understanding how things work, are often not as good at empathising.

Dr Morrison tested the theory on 40 students of psychology, an “empathising” discipline, and 40 students of engineering, which requires systemising ability.

On average, the psychology students yawned 5.5 times, compared with 1.5 yawns for the engineers in the first experiment, and in a subsequent one, the average score was 28 for the psychologists and 25.5 for the engineers.Dr Morrison said that yawning, which is often related to tiredness, may have evolved as a way of improving alertness in social groups.

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