With plants, by only planting the best known variety, and by selecting a slightly better variety when it develops, the quality will progress. If humans can with little thought modify and improve species, it takes very little imagination to view nature with the same capacity.
In addition to observing natural selection in domestic plant and animals, Darwin describes other sup-properties of evolution that he goes into much greater detail in subsequent chapters. How "variations manifestly useful or pleasing to man appear only occasionally, the chance for their appearance will be much increased by a large number of individuals being kept" (Darwin 41). Other topics he brings up are use and disuse, ant the arbitrary correlations between physical parts. The observation of this phenomenon in the domestic setting makes applications in nature much easier to accept.
Darwin begins his analysis of nature by establishing the base of which natural selection acts upon: variation. This discussion naturally leads to ways to quantify variation, which we attempt to do through terms such as species, sub-species, variety, individual differences, and Darwin's own terms "well-marked variety" and "incipient species". Of these terms, "no one definition has as yet satisfied all naturalist; yet every naturalist knows vaguely" where the boundaries lie (Darwin 44). Vaguely turns out to be an understatement when Darwin gives examples of where different experts give vastly different counts of species within a geographic area. This ambiguity portrays a system where the terms blend in with each other and a gradient occurs. .
With this fluid view of the terms, it is easier to see how a set group of plants or animals can possibly change categories. Therefore a group that shows a large amount of variation from the norm of the species, or in Darwin's terms "a well-marked variety, may be justly called an incipient," or developing species (Darwin 52).
