1. When do we start yawning? Younger than you might think! Research has shown that 11-week-old fetuses yawn as part of brain development. However, contagious yawning — as in yawning at the sight, sound or even suggestion of a yawn — doesn't happen until we are around 1 or 2 years old.
2. We know that yawning is contagious in humans, and we may yawn when someone next to us does even if we're not tired. A new 2017 study finds that yawning comes from "primitive reflexes in the primary motor cortex — an area of the brain responsible for motor function," according to a press release from the University of Nottingham, which led the research. The study also found that we have a very limited ability to resist yawning when someone near us yawns, and our urge to yawn is increased if we are specifically told not to yawn.
3. Yawns can also be contagious between humans and their dogs. In fact, even hearing their owner yawn may cause a dog to yawn. Because yawning is tied to empathy and social interaction, it underscores the close connection we have with this long-domesticated companion species.
4. Yawns last an average of 6 seconds, and on average, men yawn longer than women. During that 6 seconds, the heart rate can increase by as much as 30 percent.
5. One function of yawning is to cool down an overheated brain, which allows us to think more clearly and have better concentration. So don't worry about yawning during tests, or before athletic competitions. It'll probably help!
6. Just how contagious is yawning among humans? If someone in a group of people yawns, more than half of the group will yawn as well within a roughly 5-minute time period. (Maybe you can test this out the next time you're in a meeting!)
Editor's note: This story has been updated since it was originally published in February 2016.
Related on MNN: 15 captivating photos of animals yawning (and why they do it)