"Like confessing a murder"

The Darwin Correspondence Project has put the text of 5000 Darwin letters online. The NY Times has a number of excerpts. Here's a good one:

It was at the end of a letter to the botanist Joseph Dalton Hooker, Darwin's closest friend, that, building slowly, he dropped his bombshell of a notion in 1844, 15 years before "Origin":
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" ... 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.