Why do people yawn? Why do you want to sleep when yawning?

The cause of yawning, some scientists believe that this is the self-protection response of brain hypoxia. According to the physiological theory, when the peripheral tissue of the lung detects that the oxygen concentration in the lung becomes lower, it will make people yawn and inhale more air. But we now know that the lungs may not be able to detect hypoxia. A recent study pointed out that through ultrasonic scanning, we can see the image of the fetus yawning in the mother's stomach, but the fetus's lungs can't breathe in the womb. At the same time, experiments have proved that people yawn no more often in the environment with high carbon dioxide content than in the normal environment. Boredom theory holds that if people are bored with something, they will yawn and express their disinterest with body language. However, the activity of the hypothalamic paraventricular nucleus, known as the "yawning center" of the brain, is often related to the most interesting things. Therefore, it may be wrong to think that yawning stems from people's fatigue and boredom. According to the theory of evolution, some scientists have come to the conclusion that human yawning is inherited by primitive ancestors in order to show their teeth and warn others. Snakes crouching motionless in the grass often yawn before action; The hippopotamus in the water yawned first, and then surfaced. Since human development has entered a civilized society, yawning to warn others is out of date. If this is the case, then human yawning behavior is most likely an evolutionary relic that has lost its meaning. When physiological theory, boring theory and evolution theory can't convince everyone, a theory has basically been recognized by most people. Provine and Berninge, physiologists at the University of Maryland in the United States, have been studying yawning for more than ten years. They found that drivers who drive at night often yawn, and students who are reading books and doing their homework will yawn again and again, but few people yawn in bed. Therefore, yawning is a reaction to promote physical awakening when people feel that they must stay awake. In this sense, yawning itself is a reflection of "refreshing". A yawn lasts about 6 seconds, during which the nerves and muscles of the whole body are completely relaxed. Yawning requires facial muscle movement, so it can be suppressed by consciously biting your teeth. Jurors paid a high price for yawning that should have been suppressed, and reasonable use of yawning can also bring us benefits.