Ever wondered why watching someone yawn instantly triggers a similar urge in you to open your mouth? While scientists have understood the physiological purpose behind yawning, the reason why it is so contagious among social animals has kept them puzzled. According to Andrew Gallup, an evolutionary biologist from the State University of New York Polytechnic Institute and author of the paper, yawning could be a way for animal groups to synchronise with each other and coordinate group behaviours.

One usually yawns while shifting from one state of activity to another which can be either waking up from deep sleep or going to bed after a tiring day. Yawning has been long believed to be a means of exhaling carbon dioxide and replenishing oxygen. But, now, it appears that yawning may have to do more with the moderating blood temperature to cool down the brain. A study, published in the journal Animal Behavior, has shed more light on contagious yawns.

When it comes to successive contagious yawning between individuals, Gallup explained that this behaviour might have evolved to increase vigilance within a group. The idea is that if yawning indicates that a person is feeling sleepy then watching him yawn may alert other members of the group. This compensates for the low vigilance of the person who yawns and in turn increases the overall vigilance of the group.

To elucidate the idea, Gallup conducted a study last year. He showed several pictures to people that included threatening stimuli such as photos of snakes and non-threatening stimuli such as pictures of frogs. People were first made to see videos of yawning and then the images were shown to them. Gallup then tested their ability to pick out images from the array of pictures.

He observed that after watching people yawn, one could detect threatening stimuli or pictures of snakes more efficiently. However, the ability of people to detect the picture of frog remained unchanged, reported Science Magazine.