We have known for a long time that flowers of different plants open and close at different time of day. Yet no one really understands why flowers open and close like this at special times. It is not as simple as we might think, as new experiments(实验) have shown. In one experiment, flowers were kept in darkness. We might expect that the flowers, without any information about the time of the day, did not open as they usually do. In fact, they continued to open at their usual time. This shows that they have some mysterious (神秘的) way of knowing the time.

    Their sense of time does not depend on information from the outside world; it is, so to speak, inside them, a kind of “inner clock”. This discovery may not seem to be very important. However, it was later found that not just plants but also animals including man have this “inner clock”which controls(控制) working of their bodies and their activities.

    Human beings, then, are also controlled by this mysterious power. Whether we wish it or not, it affects such things in our life as our need for sleep, our need for food. And our ability to concentrate(集中).

    Baboons(狒狒) live in Africa. They are like monkeys. Most people think daddy baboons don't know their babies. But scientists (科学家) find that daddy baboons know how to help their babies. The daddy baboons are smart.

    Joan Silk is a scientist. She studies the baboons for 3 years. She says the daddy baboons are happy to see their babies. They have big teeth to help the babies to eat hard things. Mother baboons are small. And they live in a place. When a mother baboon gives birth(分娩), she often has only one baby. Baby baboons have fur. They are very cute.

    During the day they eat things. At night, they sleep in the trees. Most children like baboons because they look like the man.

    What is the first thing you want to do when you see someone yawn(打哈欠)? You want to yawn, too! Yawning is contagious.

    Scientists have found that all people yawn. Babies start to yawn even before they are born. The earliest yawn takes place when a baby is still inside its mother. When young children are about one year old, they start to yawn when they see others yawning. That's why scientists seem to think yawning is contagious.

    It's no secret that yawning is contagious, but why do we yawn? Well, scientists are not really sure.

    Some think we yawn because we feel bored. Recently scientists studied two groups of students between the ages of 17 and 19. One group watched music videos, and the other watched a boring color test. Scientists compared the numbers of their yawns and found that the color test group yawned more times than the video group.

    Another reason about yawning has to do with breathing. Some scientists believe that when we are bored or tired, we breathe more slowly. As our breathing slows down, we cannot get rid of(去除) enough carbon dioxide (CO₂) in our bodies. When there is too much carbon dioxide, our bodies will tell the brains (大脑) to breathe deeply. The result is a big yawn.                                                           

    In 2007, scientists suggested a new reason. They said that the reason people yawned was to cool down their brains. These scientists found that people who were warmer than others yawned more often.

    Scientists are still trying to find out why yawning happens and why it is so contagious. But they are only sure that when one person yawns, almost everyone else nearby wants to yawn, too.