Every time we see someone yawn or even think about yawning, we just can’t help but yawn too. In fact, I am yawning as I am typing this sentence! I always thought that we yawned solely because others were yawning–a mimicking reaction. However, an article featured in CNN Health, reports that scientists at the University of Vienna found that the only strong predictor of yawning was…Temperature of the Brain!! Studies showed that people are more likely to yawn when the temperature of the brain is too hot. When one’s brain temperature is too hot, studies show that yawning helps to immediately decrease brain temperature. Other factors, such as age, humidity, and hours of sleep the night before, do not have signifiant effects on one’s likeliness to yawn.
More about the experiment: http://www.sciencedirect.com/science/article/pii/S0031938414001784