Fair warning: Reading this story might make you yawn.
Though yawning is an instantly recognizable behavior shared among most vertebrate animals, scientists still don’t know enough about this seemingly simple phenomenon.
It can occur spontaneously or as the result of seeing or hearing a yawn, called contagious yawning. Most of the research on spontaneous yawning points to a physiological function: increasing blood flow to the head, oxygenating and cooling the brain. This, in turn, makes an animal more alert, particularly when it’s feeling sleepy.
But one of the biggest unsolved questions is why mammals yawn in response to one another.
In humans, research has found contagious yawning may be a form of empathizing with people experiencing a feeling, which—in the case of yawning—usually means stress, anxiety, boredom, or fatigue. Scientists have studied contagious yawning in chimpanzees, wolves, domestic dogs, sheep, and elephants—but never in lions until now.
In a new study, researchers examined contagious yawning in wild lions in South Africa. After being “infected” by others’ yawns, these lions tended to coordinate their movements.
“The data showed a clear picture: After yawning together, two lions would engage in highly synchronous behavior,” says study senior author Elisabetta Palagi, an ethologist at the University of Pisa in Pisa, Italy. (Here’s how we know animals can think and feel like us.)
This means contagious yawning could be especially important in social species such as lions, which must work together to hunt, rear cubs, and defend against interlopers, says Palagi, whose study was published in April in the journal Animal Behaviour.
For five months, Palagi and colleagues filmed 19 lions in two prides living at Makalali Game Reserve.
The results revealed the likelihood of yawning was more than 139 times higher if a lion had just seen a pride member yawning compared with not seeing the action.
Spontaneous yawning was particularly frequent when the lions were relaxed and transitioning between sleeping and waking or vice versa, the researchers observed. This supports their hypothesis that in lions, as in humans, yawning increases blood flow and brain cooling—and likely alertness. (Read how African lions are silently disappearing.)
In one of the most interesting findings, a lion would engage in the same behavior after mimicking the yawn of a nearby lion, Palagi says. For instance, if two lions were lying down, and one yawned, the other yawned. Then the first yawner stood up, and so did the other animal.
The research supports the theory that contagious yawning may have evolved to boost group vigilance among animals that live cooperatively, such as wolves and chimps, says Andrew Gallup, director of the Adaptive Behavior and Cognition Lab at SUNY Polytechnic Institute in Utica, New York.
Contagious yawning could thus “have advantages for collective awareness and threat detection,” says Gallup, who was not involved in the study.
He also agrees with Palagi that lions likely experience the same beneficial physiological impacts to the brain as humans.
Even with the new findings, Palagi is the first to admit there’s still much to discover about why animals yawn. For example, she didn’t observe whether these incidents of yawn contagion led to increased hunting success or other favorable outcomes.
Contagious yawning could serve multiple, and possibly yet unknown, functions in a cooperative animal group; for instance, gelada baboons have three distinct types of yawns that convey different messages, such as friendliness or aggression, Palagi says.
The role of empathy in contagious yawning is perhaps the most hotly debated area of yawn research, she says. Many theorize contagious yawning connects animals emotionally to each other, but there’s not enough evidence to show such a direct link.
Scientists have investigated empathy and yawning in only a handful of species, including humans, domestic dogs, wolves, and some primates. In one study, published in 2013, pet dogs yawned more in response to their owners' yawns than they did to strangers’ yawns.
The results of that study—the first to show contagious yawning between species—may indicate that dogs are emotionally attuned to their humans, the authors said.
Although Palagi’s study in lions did not directly examine if or how yawn contagion is related to empathy, she says it fills an important gap in the research linking familiarity to the propensity to catch yawns.
“If you yawn and I respond to your yawn, and immediately after we engage in the same behavior, this can improve our ability to interpret each other’s behavior,” she says.
“In this sense, yawn contagion could be important for developing higher forms of sociality.”