For many years, the atmosphere hanging over the earth's surface has tightly wrapped the temperature of life on the earth. Over time, living single-celled organisms were bred on the earth, and then multicellular organisms, plants and invertebrates were bred. After a long time, primates appeared on the earth. Humans evolved from primates. In order to adapt to the new environment, they constantly adjust and change their structures, and strive to make their legs support the weight of the whole body and make their spines stand up horizontally.