There are various theories on why we yawn, but two are most accepted.
Theory 1: Yawning keeps the brain cool.
Scientists believe that our brain works best at certain temperatures, and yawning is the body’s response to avoid brain’s overheating.
Exhaustion and sleep deprivation have been found to increase brain temperature.
When we yawn, some physiological changes such as increased blood flow & heart rate and intake of cool air reduce the brain temperature.
In various experiments, a rise in brain temperature was observed prior to yawning, and a decrease in temperatureHowever, it couldn’t be established conclusively that the drop in temperature was only because of yawning. was noticed after the yawn.
In an experiment, participants who placed warm packs on their heads were found to yawn 41% of the time when watching others yawn, as opposed to participants with cold packs on their heads, who yawned just 9% of the time (so if your head is cool, you will yawn less).
Theory 2: Yawning stretches the lungs and their tissues, forcing blood to the brain, which causes alertness.
From an evolutionary perspective, this theory explains why yawning is contagious.
When one of the primates yawned, not only did he get alert himself but he stirred up the vigilance in the whole tribe because of the contagious spread of the yawn.
Neuroscientists, on the other hand, link contagious yawning to empathy (ability to understand others’ feelings), and it starts at the age of 4-5 years (only after the ‘empathy part’ of the brain has been developed).
Damage to the region of the brain that is responsible for empathy has shown to impact empathy and proneness to contagious yawning.
We are more prone to catch yawning from friends and family than from strangers, indicating that yawning could be associated with social bonding.
Overall, while science has a clear idea of a wide range of triggers for yawning, the functional purpose of yawning and what makes it contagious are still to be demystified.
