“Disappearing” organs

　　1.5 million years ago, during the long process of evolution from the ancient ape to Homo erectus, the human body followed the basic evolution law of “common use leads to prosperity, disuse leads to decline”. Some of the dozens of organs that early humans once possessed gradually degenerated or even “disappeared” over time.
　　Where did the human tail go? The tail of
　　mammals has three major functions of maintaining body balance, using it as a tool and protecting other body organs. The functional emphasis of different forms of tails is also different. The big tail with fluffy hair and the shape of a downy stick, such as the tail of squirrels and foxes, is mainly used to stabilize the direction of movement and maintain body balance when climbing in the forest or chasing in the grassland. Fixing feathers, cloth strips and other tail decorations on the tails of bows and arrows and darts can also play the same role-without these tail decorations, the stick moving forward will deviate from the intended direction and even lose its balance in the air.
　　Tails that are slender like ropes or thick like whips, such as those of capuchin monkeys and tigers, are mostly used as auxiliary tools. Monkeys can wrap their tails around branches and hang themselves upside down in the forest to feed or sleep. The tiger’s tail is very flexible and strong. In addition to maintaining the balance of the body, the tail of the tiger is also very powerful when sweeping, which can assist the tiger in hunting.
　　As the ancient ancestors of human beings evolved from using all four limbs to standing upright with two feet, and the flexible hands can use various tools, the original three functions of the tail basically lost the value of continuing to exist, and gradually disappeared, leaving only one piece. The short tailbone is still connected to the lowest end of the spine, which can be regarded as a memorial left to the history of human evolution.
　　Decreasing body hair
　　Like most mammals, human body hair has three major functions of maintaining body temperature, reducing friction and decorating the body.
　　In the barbaric era of drinking blood, human beings maintained a constant body temperature by thick body hair all over their bodies. As humans learned to use fire, live in caves, build houses with logs, and wrap themselves in animal skins or woven plant leaves, body hair was no longer the first choice for insulation. Moreover, when hunting and running, the heat production of the human body will increase sharply. The covering of body hair is not conducive to heat dissipation, and reducing it is more conducive to survival. As a result, body hair gradually degenerates, leaving only some special parts of the human body.
　　Take hair and armpit hair, for example. There is less subcutaneous fat in the head. When exposed to the sun in summer, it is easy to cause the intracranial to heat up too quickly and cause heatstroke; and in winter, when the wind is cold and windy, it is easy to cause the intracranial to cool too quickly and affect brain function, so it is necessary to keep the hair. The presence of armpit hair is to prevent excessive friction of the skin during swinging arms.
　　Micro-organ:
　　appendix The predecessor of the appendix is ​​a section of thick intestinal pouch connecting the cecum (the initial section of the large intestine, about 6-8 cm long, located in the lower right part of the abdominal cavity), which is used to carry the crude fiber of plants that has not been fully digested in the small intestine , carry out secondary fermentation to decompose and absorb nutrients. When the human diet evolved to no longer need to eat grass roots and bark, this intestinal pouch gradually degenerated, and eventually became a micro-organ the size of a human little finger with only a little immune function.
　　Since the appendix connects to the cecum is a one-way pipe with an inner diameter of only a few millimeters, once a slightly larger block falls into and becomes embedded in it, acute appendicitis will occur. Before humans could surgically remove an inflamed appendix, it was even a fatal disease.
　　Every organ contains the mystery of human evolution. To explore the evolution of human organs is to read the history books about human evolution that lasted millions of years.