You know when a yawn’s imminent – your nostrils flare open and your mouth stretches wide. Your head points up, opening up the airway to allow the largest influx of air possible. Your hands often move up, which results in you raising your chest in order to accommodate that huge gasp of air. Even though yawning is very common, the reason we yawn is actually a complete mystery. Way back in the day Hippocrates thought yawning was a way to get bad air out of the lungs and could precede a case of the flu. While there are many hypotheses to the question why do we yawn, we really do not know for sure. Here are some theories:
To Get More Oxygen to the Lungs
The most common theory is that there is too much CO2 in the blood and this triggers a yawning response in order to bring more oxygen to the party. Sort of like ladies night at your local bar that is overrun with dudes. This theory was tested a while back when a college professor gave his students gases with a different mix of oxygen concentration, including 100% oxygen. Sadly there was no variation in frequency and duration in yawning, which suggests the CO2 theory is not the answer for why we yawn.
To Cool the Brain
A recent series of experiments at Princeton University suggest that a deep intake of breath during a yawn is to cool down your brain. The study suggests that yawning frequency is heavily influenced by the season. In winter, where the air temperature is typically much cooler than body temperature, yawning is more common because of its cooling effect. How it works is the stretching of the jaw increases blood flow to the brain. The cooler air also plays a role. The study suggests that those who are outside in cooler temperatures for longer amounts of time are the most likely to yawn.
Out of Boredom and Stress
Yawns are a social cue to communicate boredom and stress. This is why students have so much trouble staying awake during boring lectures. And then yawn due to stress before a test on material they likely slept through during the lectures!
Many primates such as baboons yawn as a display of dominance and aggression. The theory is that our ancestors used yawning for the same reason and we do it as a throwback. Even birds and fish yawn, although fish always look like they are yawning whenever they open their mouths.
Yawns are contagious!!
According to Steven Platek, Ph.D, 40 to 60 percent of the population is susceptible to contagious yawns. Again, this is presumed to be a social response and the speculation is that it is out of empathy. Interestingly enough, dogs also yawn when they see their owner yawn!