‘Oh, I can’t stop yawning. I must lack oxygen! ’ Is that statement true? It may not easy to find out the answer in our real life. We only know that we often yawn when we are tired, bored or sleepy. So if we know what causes tiredness and sleepiness, we will know why we yawn.
First, let’s see what is yawning. Yawning is a reflex of inhalation of air and the stretching of the eardrums, followed by an exhalation of breath. While yawning, your rib will lift up high so that the volume of your lungs will increase and you will get more air than usual.
Since yawning can increase air in our lung, we may yawn because we lack oxygen in our blood. This reason also causes[1] tiredness and sleepiness. Hence, when we’re tired or sleepy, we yawn for getting more air. The hypothesis is lack of oxygen in blood causes yawning.
Therefore, if the air has enough oxygen and we get enough oxygen, we will stop yawning. To proof the hypothesis, the study[2] from Department of Psychology, University of Maryland Baltimore County has conducted an experiment. They divided conditions in 4 groups: 100% of oxygen, higher carbon dioxide than normal 3% and 5%, and normal air. If the hypothesis is true, the results should be no yawning in 100% of oxygen condition and yawn frequently in higher carbon dioxide conditions. In contrast, the results showed the frequencies of yawning in each condition had no significant effects. So this hypothesis is not true!
The truth is science still cannot explain why we yawn. Occurrence of yawning seems to have many factors because you can yawn in any situation. (So, it is also a myth that we only yawn when we are sleepy, bored or tired)
Although the reason for yawning does not exist, there are some hypotheses.
1. Perking up – We yawn to perk ourselves up by stretching of muscles and joints to increase our heart rate.
2. Evolution – This is the most accepted hypothesis. The previous study[3] showed that the leader of chimpanzee uses yawning to announce sleeping time to other chimps. Other chimps will yawn contagiously to let every chimps know. Yawning is an activity that is still in our gene. From this reason, we yawn when we see others yawn. It looks like one way to communicate. This hypothesis also can explain the contagious yawning. Yawning maybe also a sort of empathy. We may laugh when we see others laugh, we may cry when we see others cry. Yawning is in the same way.
So far, yawning is a mysterious phenomenon that science still can’t explain. But if we want to find out the causes of yawning, we can cut off the hypothesis that it because of low concentration of oxygen and high concentration of carbon dioxide in our blood.
References:
1. Brian K. Gehlbach, MD; Jesse B. Hall, MD. Respiratory Failure and Acute Respiratory Distress Syndrome [online]. 2008 Jan [cited 2015 Feb 10]
Available from: http://www.merckmanuals.com/home/lung_and_airway_disorders/respiratory_failure_and_acute_respiratory_distress_syndrome/respiratory_failure.html
2. Yawning: no effect of 3-5% CO2, 100% O2, and exercise, Behavioral Neural Biology,1987 Nov;48(3):382-93.
3. Alan Neuhauser. Yawning Chimps May Offer Insight Into Human Empathy [online]. 2014 Mar 11 [cited 2015 Feb 14]
Available from: http://www.usnews.com/news/articles/2014/03/11/chimps-and-contagious-yawning-may-offer-insight-into-human-empathy
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