“Multiply, vary, let the strongest live and the weakest die” is a quote from Charles Darwin who claimed the theory of “selection natural”. Another statement of natural selection by Herbert Spencer is “Survival of the fittest”. These words indicate the features of natural selection, elimination and revolution. Natural selection eliminates genes, habits, species, and other characteristics that are inferior to others. It also carries out a revolution to adapt the environment. A characteristic to which it seems unnecessary to refer but which has remained the result of natural selection is “sleep”. While animals sleep, they do not forage, eat, find mates, procreate, or feed their young, and the animals are exposed to the danger of becoming prey. “Sleep” has survived because of its distinctive functions: rest and healing, regardless of some of the negative aspects of sleep. Although sleep has distinct functions, natural selection still requires a revolution in “sleep” to adapt to the environment. Each animal's sleep pattern was significantly altered by natural selection on three factors; times, places, methods. First, each animal's sleep time varies depending on its chosen lifestyle. Nocturnal animals sleep all day and carry out their activities at night to adapt to the climate and protect themselves from predators. Protection from climate and predators are the main reason they are nocturnal. The nocturnal animal usually lives in an extremely hot place like a desert. Although the average nighttime temperature in the desert (-3.9°C) is not mild enough for activities, the average daytime temperature (38°C) is too high that animals cannot move their bodies in this climate. As a result, they choose to sleep in burrows during the day. The...... middle of paper ......sleep habits of all animals. The three factors; time, places and methods are the main alternations of animals' sleeping habits to adapt to the habitat or to survive. The period varies from night to hibernation to long and short types. Locations are also different from water to land to nest. Finally, various sleeping methods are presented; unihemishperic, a few different sleeping postures and sleeping in a group. For these reasons, it is certain that the influence of natural selection on animal sleep patterns is changing. As a result of these changes, animals' sleeping habits resulted in diversity. Moreover, since the diversity of sleep habits is a natural selection that is equal to who lives on earth, the sleep habit of humans is not the only correct one. Therefore, the different sleeping habits of animals should not be considered special, but should be respected..