Conclusion: Inferior variation of human groups is easy to be eliminated, superior variation is easy to survive and pass on to other people.

Increase and decrease of a group of people include the birth and death of individuals in the group and the change of identity. Heredity in the people group includes narrow heredity and generalized heredity, the generalized heredity is the heredity of cultural gene. The heredity of cultural genes is not just the heredity to future generations, but also the transmission of ideas between all people, and even variations in children can be passed on to parents. 

People groups include nationality, class, stratum and organization, etc., and also include people who are classified by various other characteristics of people, such as tall people, fat people, people with certain special skills, kind people, loyal, honest people and people of different occupations. A group of people is similar to a population of organisms, and the rise and fall of a group of people is similar to the rise and fall of a population of organisms. However, reproduction of people group includes both narrow and generalized heredity.

In history, many nations, classes, strata and organizations were eliminated, such as hereditary aristocracy, slave-owning class, Xiongnu, Xianbei and other nationalities, these groups did not have reproductive and survival superiors. On the contrary, the Han nationality, intellectual class, artists and other groups have reproductive superiors and survival superiors. Their superior variations are mainly the variation of cultural genes, and the inheritance of cultural genes is mainly realized through learning after birth. It should be noted that the inheritance of cultural genes can often transcend the people groups and be shared by all people. However, many cultural genes are more easily inherited within the group, especially in ancient times, it is difficult to share cultural genes. The sharing of cultural genes is the result and symbol of social evolution. With the exception of ethnicity, nobility, caste, etc., the identity of a person cannot be determined at birth, but needs to be determined after cultural heredity.