Charles Darwin to Sir Joseph Hooker

Charles Darwin, in a letter to renowned botanist and great friend Sir Joseph Dalton Hooker, begins to reveal the idea of Natural Selection (or 'the simple way'). He says of the revelation: "It is like confessing a murder", primarily because his theory was going to challenge the entire concept of the Genesis that the semetic religion propounded.  His theory would not become common knowledge for another 15 years till the publication of On the Origin of Species.

My dear Sir
                                                   
I must write to thank you for your last letter; I to tell you how much all your views and facts interest me. I must be allowed to put my own interpretation on what you say of “not being a good arranger of extended views”  which is, that you do not indulge in the loose speculations so easily started by every smatterer & wandering collector. I look at a strong tendency to generalize as an entire evil.
What limit shall you take on the Patagonian side - has d'Orbigny published, I believe he made a large collection at the R. Negro, where Patagonia retains its usual forlorn appearance; at Bahia Blanca & northward the features of Patagonia insensibly blend into the savannahs of La Plata. The Botany of S. Patagonia (& I collected every plant in flower at the season when there) would be worth comparison with the N. Patagonian collection by d'Orbigny. I do not know anything about King's plants, but his birds were so inaccurately habitated, that I have seen specimen from Brazil, Tierra del & the Cape de Verde Isd all said to come from the St. Magellan. What you say of Mr Brown is humiliating; I had suspected it, but cd not allow myself to believe in such heresy. FitzRoy gave him a rap in his Preface, & made me very indignant, but it seems a much harder one wd not have been wasted. My crptogamic collection was sent to Berkeley; it was not large; I do not believe he has yet published an account, but he wrote to me some year ago that he had described & mislaid all his descriptions. Wd it not be well for you to put yourself in communication with him; as otherwise some things will perhaps be twice laboured over. My best (though poor) collection of the Crptogam. was from the Chonos Islands.
Did you collect sea-shells in Kerguelen land, I shd like to know their character.?
Your interesting letters tempt me to be very unreasonable in asking you questions; but you must not give yourself any trouble about them, for I know how fully & worthily you are employed.

Besides a general interest about the Southern lands, I have been now ever since my return engaged in a very presumptuous work & which I know no one individual who wd not say a very foolish one. I was so struck with distribution of Galapagos organisms &c &c & with the character of the American fossil mammifers, &c &c that I determined to collect blindly every sort of fact, which cd bear any way on what are species. I have read heaps of agricultural & horticultural books, & have never ceased collecting facts - At last gleams of light have come, & I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable. Heaven forfend me from Lamarck nonsense of a “tendency to progression” “adaptations from the slow willing of animals” &c, - but the conclusions I am led to are not widely different from his - though the means of change are wholly so - I think I have found out (here's presumption!) the simple way by which species become exquisitely adapted to various ends. You will now groan, & think to yourself ‘on what a man have I been wasting my time in writing to.’ - I shd, five years ago, have thought so. I fear you will also groan at the length of this letter—excuse me, I did not begin with malice prepense.
Believe me my dear Sir

Very truly yours
C. Darwin