Many theories have been proposed to explain why animals yawn, such as replenishing oxygen stores, cooling the brain, and even expanding the lungs.
Now, a new study claims that yawning evolved as a social signal to warn others that we’re less vigilant and that they need to be extra vigilant when searching for predators.
Meanwhile, the phenomenon known as “contagious yawning” — reflexive yawning after seeing or hearing another individual yawn — is believed to have spread this signal more widely among groups of social animals.
Because this behavior evolved thousands of years ago on the plains of Africa and is no longer applicable to modern humans, it’s possible that yawning could become extinct.
Previous analyzes have already suggested a positive correlation between yawn duration and brain size, ie the larger the brain, the stronger the yawn.
Yawning is a common trait across species, but until recently little was known about the actual function of yawning, according to a researcher at the Polytechnic Institute of the State University of New York
WHAT IS A YAWN?
A yawn is a reflex that involves simultaneously inhaling air and stretching the eardrum, followed by exhaling the air.
It is most commonly associated with fatigue and occurs before and after sleep, although tiring activities can trigger a yawn, as can a yawn.
Most vertebrates are known to yawn, and contagious yawning has been documented in humans, chimpanzees, dogs, cats, birds, and reptiles, even between species.
There are several explanations for why we yawn and why it appears to be contagious.
A recent study suggests that longer yawns are linked to larger and more active brains that get hotter.
This led the team to suggest that we yawn to cool our brains.
Instead of fatigue or inattention, we cool our mind and prepare for the next activity.
Another study suggests that contagious yawning evolved as a mechanism to keep animals, particularly prey, alert.
The study was conducted by Professor Andrew C. Gallup, a behavioral scientist at the Polytechnic Institute of the State University of New York, and was published in the journal Animal Behaviour.
“Yawning is a neurophysiological adaptation that is ubiquitous in vertebrates, and recognizing this pattern of action in others appears to be biologically important in social species,” he says in his article.
‘[It] serves as a cue that increases individual alertness and promotes motor synchrony through contagion.’
Yawning is a common trait across species, but until recently little was known about the actual function of yawning.
To learn more, Professor Gallup conducted a review of previously published scientific studies to assess the causes and consequences of yawning in groups of animals.
He researched the “psychological and social significance” of yawning in mammals and birds.
According to the research, recent studies have presented the idea that yawning is a type of social signal that warns observers that the yawning person is less alert.
Yawning, he says in his article, can be either spontaneous or contagious — the former seemingly coming out of nowhere, while the latter causes someone else to yawn.
By definition, every contagious yawn can be traced back to an originally spontaneous yawn, which is why contagious yawns must have developed only more recently.
‘There is evidence that yawning originally evolved as a spontaneous event and is therefore physiological in nature,’ said Professor Gallup.
Figure 1. Factors known to contribute to spontaneous and contagious yawning and graphs of the social effects resulting from observing yawning in others, both in (a) absence and (b) presence of yawning “contagion”
ELEPHANTS CAN ‘CATCH’ THE YAWNING OF FAMILIAR PEOPLE.
Elephants can “yawn” from people they know well, according to a 2020 study.
University of New Mexico researcher Zoe Rossman worked with a herd of captive elephants at Knysna Elephant Park in South Africa.
Handlers who yawned in front of African elephants found that they were more likely to yawn when they saw a human than any other type of human mouth movement.
While spontaneous yawning is common in all classes of vertebrates, contagious yawning is less common and has only been observed in a few animal species.
“Contagious yawning occurred afterwards and has only been documented in social species.”
Contagious yawning has only been documented in social species — those genetically inclined to associate — and develops only after infancy.
According to Professor Gallup, numerous hypotheses have been put forward to explain the physiological importance of yawning, but most lack empirical support or have been proven wrong.
For example, there is a common but incorrect belief that yawning serves to balance blood oxygen levels.
However, experiments on human subjects have shown that yawning frequency is not altered by inhaling increased or decreased levels of oxygen or carbon dioxide.
‘It has therefore been concluded that yawning and breathing are controlled by different mechanisms, and it is now widely accepted in the scientific literature that breathing is not a necessary part of yawning,’ says Professor Gallup.
Last year, researchers at Utrecht University said that yawning helps cool the brain, rather than oxygenating our blood.
They collected over 1,250 yawns from more than 100 species of mammals and birds by visiting zoos with cameras.
Other studies in humans, non-human primates, rats, and birds have all shown that yawn frequency can be reliably manipulated by changes in ambient temperature, supporting this argument.
Professor Gallup does not necessarily disagree with previous theories of yawning and acknowledges such physiological functions of yawning.
Overall, however, current evidence suggests that yawning is primarily “as a cue rather than a signal,” according to the author.
“Future studies could further investigate whether spontaneous yawning evolved specifically to communicate internal states and/or alter observer behavior in some species,” he says.
Yawning is contagious for lions too! Animals in South Africa have been found to mimic behaviors to promote group cohesion
Some animals, including humans, start yawning after someone else yawns nearby, and a new study suggests that these “contagious yawns” promote group cohesion.
Lions can make each other yawn, just like humans. But while its supposed “contagious yawn” in humans is a sign of empathy, experts say it’s a way for lions to synchronize behaviors and be a more cohesive pack
Researchers observing lions in South Africa found that the animals would not only mimic each other’s yawns, but would copy subsequent behaviors.
If a lion yawned, then got up and went somewhere else, it was almost certain that another cat would do the same.
Scientists believe that such synchronized behavior allows the pack to work as a team, finding food and detecting threats to the group.
According to researchers at the University of Pisa, animals yawn for a variety of reasons – sometimes it’s a transitional state from being awake to falling asleep, sometimes it’s a response to “high social tension”.
But a range of social animals – from wolves to birds to monkeys – have been observed engaging in “contagious yawning,” in which one member of a group triggers the yawning of another.
“Due to their high social cohesion and synchronized group activity, wild lions are a good model to study both spontaneous yawning from the physiological domain and potentially contagious yawning from the social-communicative domain,” the scientists write in a report published in the Journal animal behavior.