We all yawn. In fact, I’m yawning right now.
In humans, we yawn in order to replenish oxygen levels in the body. When our breathing slows down (this typically happens when we’re sleepy or tired and our bodies fail to consciously breathe), we tend to breathe in less oxygen and hold in carbon dioxide. This imbalance of gasses alerts the brain that we are running out of oxygen. The brain then signals the body to initiate a yawn.
When humans yawn, fresh oxygen is taken in and moved down from the oesophagus to various parts of the body. When the oxygen rushes in, the carbon dioxide is pushed out and exhaled with force. This helps the body stabilize its breathing.
But humans don’t just yawn to breathe better. We yawn to:
- Express our boredom – a very give-away physical cue.
- Keep alert – Our heart rates increase by 30% each time we yawn, sending more blood to the brain and making us more active.
- Make friends – Contagious yawns, anyone? (here’s another great insight – research shows children with autism do not find yawns contagious because they are more likely to miss the physical and social cues associated with yawning. This makes scientists believe that yawns could have a sociological significance in groups.)
What about other animals – do they yawn?
If a yawn were to mean “opening the mouth wide and breathing slowly”, then no, humans aren’t the only ones who yawn.
Research shows that over 27 different animals, other than humans, yawn. This list includes – African elephants, walruses, dogs, lions, camels, cats, sheep, gibbons, chimpanzees, rats, mice and foxes, amongst others. All of these animals engage in yawning behaviours in order to regulate their breathing.
If you’ve noticed, this list of animals mentions only one specific family of animals – Mammals. So, does that mean only mammals have the ability to yawn .i.e. breathe in to regulate their oxygen intake? Not really.
First off, not all mammals yawn in order to regulate their breathing. Baboons and Guinea pigs yawn when they’re irritated. Here, the yawn often serves as a sign of aggression, a sign that reads “Back off or I will attack.”
Then there are fish – whose normal, typical breathing behaviour resembles a big yawn. Fish also increase the number of times they yawn, when the waters they swim in have lesser oxygen and they need to breathe more to get the oxygen they need. This is a normal and daily occurrence in fishes. In comparison, human yawns occur once-in-a-while, when the body desperately needs oxygen.
Then there are Adelie penguins, who yawn as part of their courtship ritual. Their yawns also function as comfort behaviour .i.e. behaviours that animals indulge in, to make themselves more comfortable (ex: ruffling feathers, cleaning mites, grooming each other, wallowing in mud, bathing in dust etc.). The yawns have nothing to do with breathing regulation.
You may even have seen snakes yawn. They don’t do this to breathe better; instead, they do this before eating very large prey. Contrary to popular belief, snakes don’t unhinge their jaws when eating prey which are larger than they are. Instead, they yawn to make their jaws more flexible to hold their large meal.
So, what does this mean? What’s the purpose of a yawn?
The answer is – nobody knows. Not definitively, at least. Yawning means very different things to different species of animals. But there is one very interesting and entertaining piece of information that animal behaviourists have unearthed. Well, two interesting pieces of information:
- Yawns are contagious in animals too – A study showed how dogs tend to yawn when they see their owners yawn. Chimpanzees in the wild have been observed yawning when their troop-mates do.
- Primate yawns are the longest in the animal kingdom – As it turns out, the length of our yawn depends on the size of our brain. Humans are the veteran champions when it comes to yawning, clocking in an average of 6 seconds per yawn.
Want to see who our close competitors were? Read here.