Why do we yawn when we see babies yawn? The phenomenon is called contagious yawning, and it's very odd indeed.

Dogs yawn…and cats and monkeys…and even three-month-old fetuses (but not chickens). An average yawn lasts four to six seconds. We yawn more when we’re tired or bored. And trying to make it stop usually just makes another yawn pop right out. But surprisingly, we have no idea why we yawn. It’s a big medical mystery.

We also have no idea why yawns are so contagious. At around four years of age, we develop an irresistible urge to join in when we see others yawning. Children with autism, however, are an exception. The more severe a child’s autism, the less likely he or she is to catch another person’s yawn. This finding led researchers to believe there is a connection between contagious yawning and the ability to feel empathy.

However, a 2014 study by Duke University did not show a correlation between contagious yawning and empathy. It found that the older a person got, the less susceptible they were to contagious yawning.

But even so, the study's author, Elizabeth Cirulli, Ph.D., concluded that contagious yawning still remains a mystery: "Age was the most important predictor of contagious yawning, and even age was not that important. The vast majority of variation in the contagious yawning response was just not explained."

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