The uniqueness of an elephant is first manifested in its size. It is the largest living land animal, which can grow to 4 meters high and weigh 7 tons, twice as much as the second-ranked rhinoceros. Its shape is also unique, and the most striking thing is of course its long nose and huge ears. Another feature of the elephant that few people notice is that its hair is extremely rare. Hairiness is one of the characteristics of mammals. More than 99% of terrestrial mammals have fur, and elephants are a rare exception.
A science lover noticed this. I received a small paper entitled "Why the body hair of an elephant is sparse" written by him, to the effect that when Archaeopteryx grows into an elephant, the density of hair follicles on the body will naturally be greatly reduced, and the body hair of an elephant will of course become sparse. This explanation won't stand up to scrutiny. Being big doesn't mean that your hair is getting thinner. In fact, mammoths that died out 10,000 years ago have thick long hair. If necessary, existing elephants can also wear wool.
Mammoths live in the cold zone and need hair to keep out the cold; There is no need for the existing elephants to live in the tropics. So one of the reasons why elephants don't grow hair is the climate. However, many mammals that live in the same place as elephants, such as zebras, giraffes and lions, have hair. Why is the elephant's body hair seriously degraded?
Mammals are warm-blooded animals, and their body temperature must be maintained at a specific temperature to ensure normal physiological activities. For example, the elephant's body temperature must be maintained at about 36 degrees Celsius, and it is life-threatening if it is too high or too low. Body heat is generated in the process of cell metabolism, and their total amount is almost fixed, but the temperature of the environment is constantly changing. If the temperature is lower than the body temperature, then it is necessary to prevent the loss of body heat, which is the main function of hair; And if the temperature is higher than the body temperature, we must find ways to dissipate the body's heat.
Elephants live in the hottest area on earth, so how to dissipate heat is more important to elephants than how to keep warm. Because the body's heat comes from the metabolic process of cells, the more cells there are, the more heat is generated, that is, the bigger the body, the more heat is generated. Body heat is mainly emitted through the skin, and the larger the body surface area, the faster the heat dissipation. However, when animals get bigger, the volume and body surface area do not increase in the same proportion: the volume increases by the cube, the surface area increases by the square, and the multiple growth of the volume is much faster than the surface area. If you blow a balloon and increase its radius by 1 times, the volume of the balloon is 8 times and the surface area is only 4 times.
Due to the disproportionate growth of volume and surface area, considering the huge size of elephants, heat dissipation has become an extremely serious problem. The elephant is about 30 times the size of a lion, that is, it generates about 30 times the body heat, but the total skin area of an elephant is only about 10 times that of a lion, and there are still 20 times the heat to be emitted. So elephants can't keep body hair that hinders heat dissipation like lions. Similarly, the second-ranked rhinoceros and the third-ranked hippo have no body hair.
The size of elephant is about twice that of rhinoceros, but its surface area is only about 1.5 times that of rhinoceros. Removing body hair is enough for rhinos to dissipate heat, but not enough for elephants. There must be other ways to help dissipate heat. What can we do? With a pair of huge ears. Elephant's ears are not only big, but also thin. They are full of blood vessels. When blood flows through them, it is easy to dissipate heat. Especially when the ear is fanned, it is easier to quickly reduce the temperature of blood in the ear, which can reduce the blood temperature by 5 degrees Celsius. Cooled blood circulates in the body and helps to lower the body temperature.
Among the three existing elephants, the Asian elephant is the smallest, living in the north and forests, with a low temperature; The African jungle elephant is the largest, living in the sunny prairie with the highest temperature; The size and environmental temperature of African forest elephants are between the first two. Among these three elephants, the African jungle elephant is the largest, the African forest elephant is the second, and the Asian elephant is the smallest, which coincides with the statement that the main function of elephant ears is to dissipate heat.
Mammoths are bigger than the existing elephants, but because they live in the cold zone of ice and snow, the main problem they face is how to keep warm, so they need not only long hair, but also big ears. Indeed, mammoths are bigger than existing elephants except for their small ears. The ear of the largest known mammoth is only 0.3 meters long, while the ear of the African jungle elephant can be as long as 1.8 meters. It can be seen that the elephant's big ears evolved as a radiator, and its other functions (such as male elephants demonstrating with their big ears open when competing for a mate) are by-products.
Animals living in cold areas are generally larger than similar animals living in warm areas, which is Bergman's law. In cold regions, the protrusions of animals' ears are generally small, which is the so-called Allen's law. These two principles are actually generalizations of superficial phenomena, and the real purpose is to keep warm or dissipate heat.
Although the elephant looks strange, it actually contains a simple scientific truth that is not strange at all.