【英语时差8,16】生物受激后打哈欠（在线收听）

 Creatures That Yawn When Stimulated If you’ve ever visited a zoo, you’ve probably seen animals yawn. You might have thought those yawns were a result of boredom, but research has suggested that most animals do not yawn for precisely the same reasons as humans. Both humans and animals yawn to become more alert, but humans tend to yawn when they are bored or sleepy. And animals yawn in anticipation of a stimulating situation. When a human feels bored or sleepy, their blood flow becomes a bit sluggish and the brain gets less oxygen. As a result, they yawn in order to supply the brain with extra oxygen which helps them become more alert. Most research has suggested that, contrary to common belief, we don’t yawn because our brains need extra oxygen, but because we need to become more alert. Instead of yawning in order to help raise alertness levels during boring situations, animals yawn in anticipation of exciting situations. One baenninger has spent hundreds of hours observing the yawning patterns of several animal species, including lions, monkeys and humans. He found that human beings yawned most often in situations with minimal stimulation, but in which alertness was important, such as driving late at night; they yawned least often during physically stimulating situations such as an aerobics class. Captive lions and monkeys, on the other hand, yawned most often just before feeding time, one of the most stimulating times of the day. Other scientists have also observed laboratory rats yawning just prior to eating. These studies suggest that animals yawn in anticipation of stimulation rather than as a result of boredom.