Yawning helps keep people safe.
Yawning keeps people safe
Researchers have discovered that humans become more vigilant to threats if they see somebody else yawn.
It is thought that yawning evolved as a signal to a group that one of them is tired and an onlooker's brain becomes more alert to cover for the weary - and therefore more vulnerable - person.
The experts from SUNY Polytechnic Institute in New York said: "The group vigilance hypothesis proposes that seeing someone yawn should trigger neurocognitive changes to enhance the vigilance of the observer as a means of compensating for the reduced alertness of the yawner.
"The tendency to be attuned to, and affected by, the yawns of others may have evolved due to the outcome this had on enhancing survival within groups."