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 your’s | C. Darwin

Charles Darwin in a letter to Joseph Dalton Hooker, 11 January 1844.

Several items of note, Charles Darwin describes his rejection of the immutability of species as something akin to “confessing a murder.” Secondly, Darwin began to formulate his theory of natural selection in the autumn of 1938. This is important to his claim that five years prior to this letter, he would have considered himself a waste of time, keep in mind that John Dalton Hooker is one of Darwin’s closest friends, for his rejection of the aforementioned. Third, Darwin immediately mocks and rejects Lamarck. Fourth, Charles Darwin confides in someone else about his theory but he still has enough doubts to describe his work as “foolish” and “presumptuous.” By July of 1844, Darwin’s “foolish” work would produce a 230-page essay to be published at some future date and his famous memorandum to his wife,

I have just finished my sketch of my species theory. If, as I believe, my theory in time be accepted even by one competent judge, it will be a considerable step in science. I therefore write this in case of my sudden death, as my most solemn and last request . that you will devote 400 pounds to its publication. . I wish that my sketch be given to some competent person, with this sum to induce him to take trouble in its improvement and enlargement. [source]

The book wouldn’t be published for another 15 years.

Darwin Correspondence Database, http://www.darwinproject.ac.uk/entry-729 accessed on Sat Jul 07 2012