The phenomenon of contagious yawns has been linked to age, research has found.
Young people are more prone to ‘catching’ another person’s yawn than older people, a study conducted by US-based scientists has found.
Older people are less likely to be susceptible to "catch" a yawn from someone else, in comparison.
The study, published on Friday in the PLOS One journal, asked 328 healthy participants to watch a three-minute video of other people yawning. They were then asked to click every time they yawned.
The participants also underwent a number of tests to assess their cognitive function and levels of empathy, energy and sleepiness.
Overall, 68 per cent of the participants yawned. Of those, 82 per cent of people aged 25 or younger yawned, compared with 60 per cent of people aged between 25 and 49, and 41 per cent of people aged over 50.
However, scientists were unable to explain why older people were less inclined to catching yawns.
There was also no strong connection between yawning and empathy or intelligence, and age was only able to explain about 8 per cent of variability in the contagious yawn response, they said.
Researchers will now look at whether the ability to catch yawns is inherited, in the hope that understanding the gene codes for contagious yawning could highlight new treatment pathways for mental health disorders.
Dr Elizabeth Cirulli, assistant professor of medicine at Duke University in Durham, North Carolina, who led the study said: "Age was the most important predictor of contagious yawning, and even age was not that important.
"The vast majority of variation in the contagious yawning response was just not explained."
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