Time in the Animal World

　　Rhythm controls everything in Nature. ___1___.

　　The sun provides a basic time rhythm for all living creatures including humans. Nearly all animals are influenced by sun cycles and have developed a biological clock in their bodies following these cycles. The moon also exerts its force and influence on the sea. Its gravitational attraction causes the rising of the tide. ___2___. When the moon is behind the Earth, centrifugal force causes the second tide of the day.

　　Animals living in tidal areas must have the instinct of predicting these changes, to avoid being stranded and dying of dehydration. Since the time of the dinosaurs, the king crab has been laying eggs at the seaside in a set way. To avoid predator fish, the eggs are always far from seawater and protected by sand. In the following two months, the eggs undergo dramatic changes related to the cycles of the moon. When the second spring tide comes, the young king crabs have matured. ___3___.

　　Most of the mammals, either the giant elephant or the small shrew, have the same average total number of heartbeat in their lifetime. Shrews live only for two and a half years, and spend their life at a high speed and high tempo. Animals like shrews with a pulse rate of 600 per minute have an average total of eight hundred million heartbeats throughout their life. The African elephant has a pulse rate of 25 beats per minute, and a life span of 60 years. The size of the body determines the speed of life. ___4___.

　　As we get older, our sense of time is being influenced by the physiological changes of our body. The elderly spend more time resting, and do few sports. ___5___. For a child, a week is seen as a long time.

　　练习：

　　A．For an adult, time goes fast year by year.

　　B．It controls, for example, the flapping of birds' wings, the beating of the heart and the rising and setting of the sun.

　　C．The larger the animal is, the longer its life span is and the slower its life tempo is.

　　D．The tide goes out when the moon moves away and its attraction is weaker.

　　E．We always tend to think all the animals have the same sense of time as human beings.

　　F．The second spring tide takes them back to the sea.