“As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.”

This is the book’s first presentation of the concept of natural selection. The concept is fundamental to Darwin’s entire theoretical enterprise, and he develops it thoroughly throughout the book. Darwin’s inspiration was, in part, Thomas Malthus’s Essay on the Principle of Population, which discusses the laws of population growth. Darwin applies these ideas to the natural world and discusses how the slightest adaptable variation in an individual can eventually lead to a major change in that species.

“Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained—namely, that each species has been independently created—is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species.”

Here, Darwin boldly asserts his rejection of the (then-common) view that species were created independently of one another—or that, among other things, they didn’t evolve from common ancestors. In addition, he claims that species aren’t static forms, timelessly reiterating themselves in succeeding generations. Instead, they’re mutable iterations of dynamic processes. In Darwin’s time, this view was highly contentious within the scientific community and deeply upsetting to dominant Christian religious convictions.

“[…]namely, that we know nothing about the origin or history of any of our domestic breeds. But, in fact, a breed, like a dialect of a language, can hardly be said to have had a definite origin. A man preserves and breeds from an individual with some slight deviation of structure, or takes more care than usual in matching his best animals and thus improves them, and the improved individuals slowly spread in the immediate neighborhood. But as yet they will hardly have a distinct name, and from being only slightly valued, their history will be disregarded. When further improved by the same slow and gradual process, they will spread more widely, and will get recognized as something distinct and valuable, and will then probably first receive a provincial name.”

Darwin explains why the origins of specific domestic breeds are unknown and, more fundamentally, why speaking of a specific origin point for a breed makes little sense. Changes don’t inherently result from any intrinsic characteristic of a breed but instead from the attention of human breeders.