The yawn itself is simple. Suddenly we feel the need to open our mouth wide. Within a few seconds, the muscles of the jaw and torso are tensed strongly and a huge amount of air rushes into the lungs with lightning speed. Then we exhale quickly. We all yawn, including almost all animals with vertebra and decoder. We do it spontaneously and several times a day, and we already start yawning in the womb.
As simple and obvious as yawning is, no one still can explain with certainty the reason for yawning. A popular hypothesis is that we yawn to cool our brains. Brains work less when threatened by overheating, so we bring cooler air into our heads with a good yawn to cool the brain. “But in fact, there is very little scientific research to confirm this hypothesis,” says physician Chris Doelman of Tergooi MC in Hilversum, the Netherlands. Doelman combined studies on yawning and came up with another possible hypothesis: “We yawn a lot when we’re tired. At that moment our muscles relax, including those in the throat. This narrows the pharynx and makes breathing less efficient. Compare that to breathing through a straw. The body may respond by yawning, In order to enlarge the pharynx again and keep the muscles awake.
Doeleman finds it inconceivable that yawning cools our brains. Some of the studies that find this are based on experiments in which students held a warming bag over their heads. The students yawned with a warm bag on their heads. You can infer that heating the brain is the trigger, but on the other hand, you also get sleepy from a warm bag on your head. And when we have a fever, we actually yawn less, even though our body temperature is higher.
The fact that our body wants to compensate for the incorrect muscle tension in the throat by yawning can also explain why people yawn more often when they are stressed. “Athletes, for example, sometimes yawn while getting ready for a sprint. They are not tired, but they are experiencing stress that puts their respiratory muscles under a higher strain. This is how the pharynx also narrows. Then yawning helps the muscles relax.”
Doelman stresses that this is just a new hypothesis. It’s an alternative explanation, but in fact more research is needed to really explain why we yawn. It may be interesting to better visualize yawning, for example with the help of direct MRI (Moving Pictures, ed.). In this way we can see the contribution of all muscles to yawning.
Why do we yawn when we see others yawning? This may be an even greater mystery. People, dogs, and monkeys yawn when they see someone else yawning. Therefore, it is possible that yawning has a social function in addition to its main function. On the other hand, different animal species give different meanings to yawning. Sometimes it is an expression of aggression, sometimes it is something sexual, and with us, for example, it is rude to yawn too. Whatever the social explanation, yawning is a useful communication tool. I think it makes perfect sense for pack animals to know that your comrade or opponent is tired.
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