It is well-known that the influence of the breeder and of Malthus was the two major conceptual sources of the theory of natural selection. Darwin recollected that he found the possibility of explaining the process of species formation through the breeder's principle of selection and then realized how to apply this principle to that problem in the course of reading Malthus' An Essay on the Principle of Population. But recent studies on Darwin's notebooks showed that the influence of these elements appeared in reverse order. In other words, Darwin acquired the mechanism of species formation through Malthus' concept of the struggle for existence, and then arrived at the concept of natural selection by reinterpreting this mechanism through the breeder's work. This new interpretation on Darwin's path to the discovery of natural selection showed the fact that the role of the breeder's concept of selection was not to acquire the mechanism of species formation but to interpret and describe the acquired mechanism. The purpose of this article is to investigate synthetically the influence of the breeder on the theory of natural selection along the line of this interpretation. For this purpose, I consider the breeder's influence which appeared during the process of the development of this theory in Chapter 2. And in Chapter 3, I consider the influence of the breeder's work which was reflected in a finished theory that appeared in the Origin of Species. Lastly, in Chapter 4, I consider the influence of the breeder on Darwin's vision of nature.