Why are yawns contagious?

Answer 1

We can't say for sure, but there are several possible explanations.

One potential explanation comes from research out of the University of Nottingham, which suggests that contagious yawns are prompted by automatic, primitive reflexes in the part of the brain responsible for motor function.

Other researchers think it has something to do with empathy or social cues.

"Researchers have seen that yawning may not be as contagious to people with autism or schizophrenia," Meredith Williamson, clinical assistant professor at the Texas A&M College of Medicine, told Vital Record. Individuals with these conditions can struggle with empathy.

A 2013 study did find, however, that children with autism experienced contagious yawns as often as non-autistic children when made to focus on the yawner’s face, suggesting social cues, rather than empathy, are at play.

"It's multifactorial," Williamson said. "It could be partly an innate form of communication or it could be related to empathy, or a bit of both combined with other factors." Further research would be needed to pin down the exact causes.

Answer 2

Some people have a theory about why yawns are contagious, but it has since been proven incorrect. The theory goes like this... When you breathe, you take in carbon dioxide. Scientists used to think you yawned because you had too much Co2 in your body, and you yawned it out. When you yawn near someone else, scientists thought that they then breathed in the cloud of Co2 and then needed to yawn it out. And the theory was that when you are tired you take shallower breaths and so need to get rid of more carbon dioxide. This has recently been proven a false theory. However! When you talk to plants, it really does help them grow because you are giving out Co2 as you breath, which helps them to grow quicker.
They're contages as yawns contain a small amount of nicotien this erges people to yawn to get their fix.