In the past, Darwin and many scholars expressed the theory of natural selection very complicated, not accurate and clear, Fang Zhouzi's expression is the most concise, including not only the description of the principle of natural selection and the principle of survival struggle, but also the reasoning and proof process of these principles. But there are still three problems with this formulation of natural selection:

    First, what is superior variation and what is inferior variation need to be strictly defined.

Second, there is a major premise implied in the derivation of corollary 2, that is, the condition that any organism can survive in nature is that the rate of reproduction of this organism is greater than or equal to the rate of death. The principle of natural selection is often expressed as survival of the fittest, so what is the fittest? Some people say that the fittest is able to adapt to the environment, what is called to adapt to the environment, is able to survive. This is tautology. The real meaning of survival of the fittest is that only when the rate of reproduction is greater than or equal to the rate of death, such creatures can survive in nature.

Thirdly, the natural selection and the struggle for survival are two independent principles, and the struggle for survival is not a prerequisite for natural selection. At certain times in history, when resources were relatively abundant, the vast majority of organism's offspring can survive, and the natural environment still selected organisms. However, the result of natural selection may not be the evolution of organisms, and the inferior organisms can survive.

Therefore, the principle of natural selection of organisms should be modified as follow.

(1)The Principle of Natural Selection of Organisms:

Major premise: the condition that any organism can survive in nature is that the rate of reproduction of this organism is greater than or equal to the rate of death;

Minor premise: There are heritable variations among the offsprings of organisms; Some variations make organisms reproduce faster than other organisms, which is called having greater reproductive capacity; Some variations cause organisms to die at a slower rate than others, which is called as having greater survivability. The variation with greater reproductive ability and greater survival ability is the superior variation, and the opposite variation is the inferior variation.