字幕表 動画を再生する 英語字幕をプリント Hey, Vsauce. Michael here. And today we're going to talk about yawning. Why do we yawn and why is yawning contagious? How come when I see someone yawn or even think about it it makes me kinda of want to yawn? First things first, definitions. When you yawn, you inhale air and stretch your ear drums. That's why your ears pop when you yawn. Now, if you yawn and at the same time stretch your whole body, that is called pandiculation. A common misconception about yawning is that people yawn when they need more air, more oxygen. But studies have shown that no matter how much oxygen is in the air around a person, they won't yawn more or less frequently. And when people exercise and their bodies do, in fact, need more oxygen, they don't yawn more often. Instead, research has shown that our first answer most likely lies in being cool. When you are exhausted, tired, deep brain temperatures increase, but your brain is like a computer - it operates best at a very specific temperature. And so yawning, bringing all this outside air in through your ears and your mouth, cools your facial blood and actually helps cool down your brain. This phenomenon is particularly easy to observe when parakeets yawn. Researchers have found that parakeets only yawn within a very specific range of temperatures. Too cold outside and yawning will cool the brain too much. Too hot and yawning will actually warm it up. Parakeets are perfect test subjects for this effect, because they yawn just like you and me, except they don't exhibit contagious yawn. If you show a person a video of other people yawning, it's likely that the person watching will yawn his or herself, unless you put an ice pack on their forehead, keeping their brain cooler. Seriously. The University of Albany has found that people contagiously yawn less frequently when they have ice packs on their head, which means that yawning to cool your brain isn't just for the birds. Studies have shown that yawning also increases blood pressure, stretches facial muscles and increases focus. When you panticulate, you stretch all of your muscles, making them better ready to be used at any moment. So when it comes to a herd of prey animals, contagious yawning make sense, because a herd that yawns together stays alert together. Under this theory, yawning is advantageously contagious, because that first animal to yawn acts as a sort of reminder to the rest of the herd to keep themselves ready and alert. But, of course, when we say that yawning is contagious, we don't mean like a disease. Instead, it's a bit more closely related to empathy. Sympathy is when you are concerned for others, where you wish someone was better off. Empathy is the ability to recognize and share the emotions that other people feel. Emotional contagion is when the emotions of people around you influence the way you feel without you even having to separate yourselves from them, like when being around happy people lifts your spirits or how anger and fear can lead to mob mentality. Now, children with autism, who exhibit impaired social interaction and communication, yawn less frequently than other children when viewing videos of people yawning. So, is yawning an emotional contagion or is it about empathy? Well last year, the University of Pisa found that yawn contagiousness is greatest with family and then friends and then acquaintances and lastly strangers. And a study at Leeds University brought in participants to take a test that measured how empathetic they were. But before the test began, amongst them was one person who worked for the researchers and this person yawned every minute for 10 minutes. Interestingly, the people who wound up scoring the highest on the empathy test were also the ones who contagiously yawned along the most. Let's talk more about animal yawning. What fascinates me so much is that animals across many species all yawn, but they do so for different reasons. Animals like guinea pigs and some monkeys yawn to intimidate and show their sharp scary teeth. Some penguins yawn to attract mates and when snakes yawn, it seems to be about realigning their jaws and opening their tracheas to breathe better after a big body disfiguring meal. Fish yawn more frequently when water oxygen levels are low or water heat levels are high. So, when you yawn you're participating in the behavior shared across all kinds of animals, but most likely you're yawning for purposes unique to your species - us humans. What's really cool is that yawning is most likely an ancient signal telling the rest of us humans "let's do this, let's survive." And as always, thanks for watching.