The mystery of why yawning is contagious may finally have been solved: an Italian study says it’s linked to empathy.

Suggesting yawning may show the closeness of your relationships rather than simply how tired you are, scientists discovered people were more likely to yawn in response to a close relative rather than just a friend.

Since the act of yawning increases blood flow around the brain, the research indicates contagious yawning may have evolved as a way of maintaining alertness within a group.

Dr. Catriona Morrison, an experimental psychologist from the University of Leeds, said that yawning when those around you do so is a primitive subconscious response that could shed light on the evolution of the human brain.

“Some have suggested that it developed from the days of cavemen when someone had to be on watch all the time,” she said. “Social behaviour is thought to be a conscious function of the brain, but this is unavailable to consciousness. We just don’t have any control over it at all.”