Sexual reproduction, a way of reproduction, has a long history. Probably from ancient microorganisms more than a billion years ago. Microorganisms eat each other. By chance, a gene fragment of an organism will be preserved in another bacterium and gradually evolve into a plasmid, chloroplast, mitochondria and other organelles, which can be copied and inherited and undertake some biological functions.
Because combining the genes of two individuals can theoretically combine the genetic advantages of both sides and make the organism adapt to a more complex and changeable environment. The reproduction of species depends on the population, and whether the population can continue normally. After the emergence of multicellular organisms and even large animals and plants, such reproduction methods have also been inherited. When humans appeared, life on the earth was already flourishing. Humans and even apes that have evolved into humans have maintained such a reproductive model. Without men or women, the reproductive process cannot be realized and human beings will become extinct.
The evolution of species depends on the population, and only in the population can there be enough individuals. Because of the difference of individual genes, the offspring genes produced by mutual combination are more diverse and can adapt to slightly different environments. However, this little difference has become the reason why human beings finally survive in a complex environment.
Another point depends on the population size and scope of activities. If the initial human population is too small, mate selection will be concentrated, leading to serious inbreeding problems. Finally, human beings will have a large number of reproductive defects, and the number of individuals who died in their early years will increase. The extinction of mammoths is related to this, which requires human beings to have a large enough activity area.
At first, after humans were separated from other apes, there was no long-term reproductive isolation, and there were still some reproductive phenomena. Neanderthals are an extinct human branch closely related to Eurasia, because the coexistence and reproduction of modern human ancestors and Neanderthals can ensure the diversity of human genes and increase human ability to adapt to the environment.
Genetic diversity is also a reason why scientists believe that human beings originated in Africa. At the genetic level, the genetic diversity of human groups in Europe and Asia is even worse than that of some tribes in Africa. From the perspective of gene continuation, it can only explain that some primitive humans left Africa to make a living elsewhere because of the competition for survival. The history of human reproductive process and evolutionary migration determines that human beings naturally appear together with men and women.