By The Fireplace...
The Origin of Species by Charles Darwin
Chapter I. Variation Under Domestication
Character of Domestic Varieties; Difficulty of distinguishing between Varieties and Species; Origin of Domestic Varieties from one or more Species
Chapter II. Variation Under Nature
Species of the larger genera in each country vary more frequently than the species of the smaller genera
Many of the species of the larger genera resemble varieties in being very closely, but unequally, related to each other, and in having restricted ranges.
Chapter III. Struggle for Existence
Chapter IV. Natural Selection; or the Survival of the Fittest
The Probable Effects of the Action of Natural Selection through Divergence of Character and Extinction, on the Descendants of a Common Ancestor
Chapter V. Laws of Variation
A part developed in any species in an extraordinary degree or manner, in comparison with the same part in allied species, tends to be highly variable
Distinct species present analogous variations, so that a variety of one species often assumes a character proper to an allied species, or reverts to some of the characters of an early progenitor