Thirteen-year-old Alexis from St. John, NB has emailed to ask what causes people and animals to yawn, and whether yawning helps us in any way. There are certainly lots of assumptions about yawning and if we are not careful about when and where we yawn, we can unintentionally insult people. Guests may think we want them to leave so we can get some sleep; a teacher who has been enthusiastically explaining the quadratic formula, may think we are saying he is boring us.
There are two kinds of yawn common to humans and other species capable of intelligent and affectionate responses. One of them is spontaneous and is triggered by stress, boredom or fatigue. The other is known as empathetic yawning and happens when other people, or our dogs maybe, are yawning, causing us to yawn too.
The good news is that even if we yawn when we are sleepy or bored, our host or teacher should feel complimented rather than insulted. Since the brain consumes up to one-third of the energy we take in, it generates heat. Psychologists discovered that yawning increases blood flow to the brain and draws in cooler air which is needed for clear thinking and mental efficiency. We could just drift off to sleep, but if our body chooses to yawn instead, we are really indicating our desire to remain alert and engaged. Alternatively, we could put an ice pack on our foreheads. That would work as well as a yawn, but may be seen as even more insulting.
The second type of yawning is not usually seen in children under four, though spontaneous yawning is, and occurs even in the womb. Most facial responses to emotional conditions, such as happiness or sorrow are picked up by those around us and are reflected subconsciously in the faces of those who care about us. Similarly, when people around us yawn, we yawn with them, and so do chimpanzees, but only in their own social milieu. Unlike chimpanzees, most people would probably yawn in response to yawning animals as well because we tend to see all other living beings as fellow travellers and all other people as part of our human family. However, we do yawn back readily if the first yawner is someone we love. We exchange yawns with friends a little more hesitantly, and with acquaintances even less spontaneously. Yawns from strangers do elicit a yawn from us, but unpredictably.
It is very likely that both spontaneous and empathetic yawning evolved for the protection of groups in potential danger. It is common knowledge that everyone is safer "when cooler heads prevail".