People yawn, but not just when they are sleepy. Humans seem to "catch" a yawn when someone near them yawns. Chimpanzees and baboons also yawn for the same reason. Even dogs do. But why?

Scientists believe it is a sign that these animals are capable of empathy - feeling what other animals feel. A new study of wolves suggests it is more common among animals than experts had realized.

Humans and other primates are more likely to catch a yawn when they are around those with whom they share "a close social bond." In people, catching a yawn is more common among those who get high scores on empathy tests. Scientists found it is less common among those with mental conditions that cause them to have less empathy.

Yawning is also contagious for dogs. But there's a twist: They don't yawn in response to yawns from other dogs, but to yawns from people. What's more, the yawns are more contagious when the person doing the yawning has a strong emotional connection to the dog.

A Trip To The Zoo

A group of scientists in Japan wondered if the close connection between dogs and humans set the dogs apart from other animals. Do some other animals, aside from the primates, catch yawns too?

Dogs are "unusually skilled" at reading human behaviors, the University of Tokyo scientists noted in their study. The researchers believe "it could be possible that dogs' ability to yawn contagiously evolved with the capacity for reading human communicative signals."

On the other hand, if dogs were born likely to catch yawns, then wolves should be too. Wolves are the closest living relatives of dogs. Like dogs, they are also "highly social," the researchers wrote.

So off they went to the Tama Zoological Park, a zoo near Tokyo. In the park was a pack of 12 wolves. There was a mother, a father and their 10 offspring (five males and five females). The researchers spent 254 hours observing the wolves over a five-month period, paying special attention to instances of yawning.

The researchers only studied certain wolf yawns. They looked at yawns that occurred when wolves were awake and relaxed, and not in distress. When they spotted such a yawn, the researchers noted the wolf involved, the other wolves nearby, and where the wolves were looking when the yawn occurred.

Then the researchers watched the nearby wolves for the next three minutes to see if any of them yawned too. If they did, they noted the time between the initial yawn and the follow-up yawn.

Strong Social Bonds

The researchers also watched the wolves for three-minute periods that did not start with a yawn. They wanted to make sure the wolves didn't just yawn at any time.

The scientists found that the wolves were indeed more likely to yawn after another wolf near them yawned. Yet, a yawn was more likely to cause a follow-up yawn if the two animals had a strong social bond. Not only that, but among females, the closer the bond, the shorter the gap between the first and second yawn.

Yawns were also more likely to be contagious if they could be seen, not just heard.

"Yawning in wolves is contagious," the scientists concluded. They say it makes sense. For a highly social animal such as the wolf, coordinating activities "promotes social cohesiveness of the pack."

Yawns between friendly wolves were more catching than yawns between wolves who were not friends. The researchers think this proves that wolves feel empathy, and that other animals may as well. They wrote that "empathy might be present in a wide range of species."