No-one is sure why we yawn, although we do know that it increases levels of dopamine and serotonin in the brain. Yawning's not an activity restricted to humans, however.Mammals and other animals are also known to yawn... but do they catch yawns from one another and can they catch them from humans?
What are yawns?
A yawn is a reflex in which a person – or animal – opens their jaw wide open, taking in a sharp, deep intake of breath and then a quick exhalation.
Yawns tend to strike in moments of tedium or sleepiness. But these involuntary muscle contractions, involving an open mouth and a deep intake of breath, are anything but boring.
Why do we yawn?
Yawns are mysterious things. The debate around their function remains… er… wide open. There are physiological possibilities, including the regulation of brain temperature or oxygen levels.
Or perhaps the function of a yawn is a more social one – synchronising group behaviour, for example, or signalling empathy with others.
Why are yawns infectious?
Just as we're not entirely sure why we yawn, we also don't really know why we seem to 'catch' them from one another. There are several theories as to why this might happen, with some believing that contagious yawning keeps people in the same state and sleep cycle, so we are able to work together.
Another study suggests that yawning is a symptom of the brain's requirement to regulate its temperature.
Do animals yawn?
Yawning occurs in all sorts of animals, from budgies to baboons, and have been linked to a range of functions, from stimulating alertness to co-ordinating group behaviour.
In South American sealions, according to new research, yawning seems to be a signal of anxiety, occurring after aggressive interactions between individuals.
“Our data show that, just after an agonistic event, there is a peak of yawning in the aggressor and the victim, which may reflect anxiety of the subjects, or may function as a stress-releaser mechanism,” says Clara Llamazares-Martín of Spain’s CEU Cardenal Herrera University.
The findings chime with work on apes and monkeys, showing that yawning is more frequent in socially stressful situations.
It might turn out that, in sealions, it serves to defuse social tension between adversaries. The team is now working on whether their yawns are contagious, like they are in humans and other apes. If that were the case, it would be evidence that sealions have a capacity for empathy.
Do animals yawn when humans yawn?
The contagiousness of yawns is good evidence that social behaviour is at least part of the story. So powerful is the urge that, in humans, it can be elicited just by hearing someone yawn or even talking about it.
Chimps, baboons, wolves, sheep and budgerigars are all prone to catch the yawning bug. And yes, some animals, including dogs, chimps and elephants are inclined to catch it from a human.
Chimps will even do the same in response to a yawning robot. Intriguingly, dogs can catch yawns from humans, but not from other dogs.
All of which probably raises more questions than it answers.
Do animals catch yawns off each other?
Contagious yawning in humans and primates has been linked to our evolutionary capacity for empathy and social bonding, but other mammals also find yawning catching. Studies of domesticated dogs have shown that they often mimic human yawning, while a pack of wolves in a zoological park in Japan was observed to have yawn contagion by a team from the University of Tokyo who were studying them. The frequency of yawning was linked to how closely the first yawning wolf was associated with the others. The closer the bond between the animals, the more likely the yawn was to be catching.
That both wolves and domesticated dogs find yawning catching suggests that this ancestral trait is not confined to humans. If you yawn and your dog copies you, then it is probably reinforcing the emotional bond between you.
