The main content of natural selection theory is that organisms have strong reproductive ability and can produce a large number of offspring, but environmental conditions (such as living space and food) are limited, so some individuals must be eliminated.

The eliminated organisms cannot reproduce their offspring, so they cannot inherit their own traits. Accumulated from generation to generation, the biological clock group evolved.

Mutation and gene recombination produce the raw materials of evolution.

Natural selection determines the direction of biological evolution.

Isolation leads to the formation of new species.

For example, the inchworm used to be all white, and later it mutated into black (the raw material for mutation and gene recombination evolution). The original black color will die, because it is not a protective color, but because of industrial pollution, the bark becomes black, and black becomes a protective color, so it is possible to reproduce (natural selection determines the direction of biological evolution), and slowly, more and more people survive.