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There are four main sources of evolution. They are genetic drift, gene flow, mutation and natural selection. Each of them has its force to influence people`s development. Natural selection is one of the first known forces. It is trying to explain some peculiarities of species, underlining their struggle for existence, skills and peculiarities obtained in this struggle. Later, with the discovery of genes the theory of genetic drift was introduced, which stated that genes and their change play a leading role in the process of evolution, while mutation is the main power, which changes certain genes by the environment.