When thinking about why we yawn, people mostly pay attention to the respiratory, or breathing, aspect. When breathing, we inhale to increase our oxygen supply, and we exhale to get rid of excess carbon dioxide. So, the deep breath that accompanies yawning has led many people to believe that the purpose of yawns is to increase oxygen levels. While this explanation seems to make good sense, research conducted 30 years ago firmly rejected this idea. In a clear test of whether yawning was caused by low oxygen levels, Dr. Robert Provine et al. designed an experiment in which they changed the content of the air that was inhaled by participants in the laboratory and then witnessed the effects that the air had on yawning. The researchers had separate conditions where participants either inhaled air with extra oxygen or extra carbon dioxide. These experiments demonstrated that neither breathing pure oxygen nor increased levels of carbon dioxide altered the rate of yawning in humans. In other words, the results of this study revealed that yawning was unaffected by the amount of oxygen in the air, and that yawning, and breathing are controlled by separate mechanisms.

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