Yawns spread more easily between family and close friends, and from high-status monkeys to those lower on the totem pole, according to a study published online today (Nov. 14) in the journal PLoS ONE. This pattern of social yawning mimics one found in humans and suggests infectious yawning is a byproduct of empathy, which coordinates emotions in a group.

"It underlines that the mechanism of yawn contagion in the two species is the same," said study co-author Elisabetta Palagi, a primate researcher at the University of Pisa in Italy. "One of the possible functions of yawn contagion is to synchronize individuals of a social group. In humans, yawn contagion is extremely important but just between people who share strong bonds."

Many animals spread yawns: Chimpanzees and baboons catch them from each other,dogs can catch yawns from their owners, and even parakeets yawn contagiously.

In humans and chimpanzees, contagious yawning follows social rules: People yawn if friends do, but not if a complete stranger does. Those who haven't mastered empathy, such as babies (of the human, canine and chimpanzee varieties) don't yawn infectiously, and neither do children with autism.