"Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species," (Darwin) Darwin begin his discussion of how Natural selection benefits a species by questioning what natural selection is. After he establishes what Natural selection is he launches into his argument how it improves and sustains the species. Finally Darwin speculates how man could use Natural Selection to improve domestics animals.
Darwin begins by questioning why there are variations and adaptations within species and where they originate. He observes how a species survives perilously by adapting to its environment. He sees it "in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird" (Darwin) in "the structure of the beetle which dives through the water: in the plumed seed which is wafted by the gentlest breeze." (Darwin) Darwin says when a species attains a quality that "tends to the preservation of such" (Darwin) an individual, the member has a better chance of surviving and passing that trait on to its offspring. While not all of the offspring survive those who inherit the trait have a better chance of surviving. Darwin calls "this principle, by which each slight variation, if useful, is preserved," (Darwin) Natural Selection. .
Darwin next establishes what he believes falls under Natural Selection or the Struggle for Existence. His definition is very broad. Two creatures physically embattled, is a struggle for existence. A plant at odds with a harsh environment is said to struggle for existence. Different species competing for the same niche can be said to be struggling for existence. There can also be a struggle between a species itself when there is overpopulation in a limited space. (Darwin) .
Finally Darwin proceeds to explain how Natural Selections is present in nature. He begins by dispelling the misconception that man creates the variability in traits in animals through domestication.