Darwin rejected the idea of creation because of his own personal beliefs and sought an explanation that did not include a supernatural being. Thanks for your posting, though I don't think the above bit is quite accurate. Darwin did not set out to reject the idea of creation (indeed, at one point, he was studying to be a clergyman), held conventional religious beliefs of his day throughout his 5-years as ship's naturalist on board HMS Beagle, and only formulated--reluctantly--his theory of speciation years later, when he came to evaluate the data he had gathered. Whether you agree with Darwin's interpretations or not, I don't think it can be held that Darwin set out to reach specific conclusions, he was following the evidence, at least as he best understood it. If anything, abandoning religious tenants he had held in youth was painful to him (not least because of the distress he feared it would give to his wife, Emma Wedgewood), though it may be relevant that the tragic loss of one of his daughters made him even more sceptical of a benevolent diety.
Janet Browne's biography of Darwin is a magnificent read, whatever views one may hold of Darwin's work.
There is plenty of evidence that Darwin was in fact an atheist from both his own writings and from those who knew him. A simple google search can provide that.
In regards to his pushing aside the idea of a creator in favor of his own theory, you can read it in "Origins" when he discusses the eye.
To arrive, however, at a just conclusion regarding the
formation of the eye, with all its marvelous yet not absolutely
perfect characters, it is indispensable that the reason should conquer
the imagination; but I have felt the difficulty far too keenly to be
surprised at others hesitating to extend the principle of natural
selection to so startling a length.
In living bodies, variation will
cause the slight alterations, generation will multiply them almost
infinitely, and natural selection will pick out with unerring skill
each improvement. Let this process go on for millions of years; and
during each year on millions of individuals of many kinds; and may
we not believe that a living optical instrument might thus be formed
as superior to one of glass, as the works of the Creator are to
those of man? Regards,
Boiler Plate