The Origin of Species by Means of Natural Selection: The Preservation of… (original: 1859; edição: 1982)

Introduction
by David Quammen
On the Origin of Species is a surprising, peculiar work in many ways but among all its peculiarities my favorite is this: Seldom in the history of English prose has such a dangerous, disruptive, consequential book been so modest and affable in tone. That's because its author, Charles Darwin, was himself a modest and affable man—shy in demeanor though confident of his ideas—who meant to persuade, not to declaim or intimidate. You can hear it in his opening sentences:
When on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers.
He sounds lik a gentle uncle, clearing his throat politely, about to share a few curious observations and musings over tea.

Introduction
When on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.