Today, there are many theories about the contagiousness of yawning, as this issue has interested mankind since ancient times. Interestingly, yawning lasts 6 seconds with an average frequency of every 68 seconds.

According to English scientist Malcolm Weller, human evolution linked contagious yawning to a signal that animals used to indicate it was time to return for the night.

The American scientist Ronald Benninger also agrees with this theory, adding that our ancestors synchronized their rest and activity with yawning. Researchers also ran an experiment where students watched yawning videos for the same duration and found that only the most empathetic students yawned.

Magnetic resonance tomography showed that these students had high activity in the areas of the brain responsible for empathy. Therefore, studies have shown that viewing photos or videos of yawning can provoke the contagion of yawning.

Researchers at Duke University have found that the contagion of yawning may decrease as people age. For example, people with autism or schizophrenia do not experience contagious yawning, nor do children under four.

Scientists proved that humans, chimpanzees, and some species of monkeys are exposed to yawning contagion, and all other animals, even fish, yawn without realizing it. Another interesting fact is that strangers will not yawn when they look at someone.