Despite the many myths spread by various groups, Darwin was never an atheist. Nor did he ever leave his church (although he did stop attending it). In fact, Darwin was formally trained as a priest, and believed throughout his life in god.
You can read all about it in his own words, in his autobiography which was published post-posthumously:
http://darwin-online.org.uk/content/frameset?itemID=F1497&viewtype=side&pageseq=1
Bryan
The truth of the matter, as with many truths, is a bit more complicated. Darwin's views on religion evolved (if I may use that term) during his life, he moved along a continuum from a rather ordinary, typical believer in Christianity to a doubter and finally a rejector.
This process was complicated by by his wife's firm belief, the social processes and norms of the time that made the church the center of local social activity, his close friendship with the local Vicar with whom he engaged in various charitable works and his intense intellectual and personal animosity toward the Vicar's replacement.
But look at the quotes for a moment, in their temporal sequence:
As a child he wrote: "... but when in doubt I prayed earnestly to God to help me, and I well remember that I attributed my success to the prayers and not to my quick running, and marveled how generally I was aided" (Life and Letters of Charles Darwin, D. Appleton and Co., New York, 1911, Vol. 1, p. 29.)
After giving up his medical studies and embarking on a theological degree with the intent of becoming a county pastor he wrote: "I liked the thought of being a country clergyman. Accordingly I read with care Pearson on the Creed and a few other books on divinity; and as I did not then in the least doubt the strict and literal truth of every word in the Bible, I soon persuaded myself that our Creed must be fully accepted." (Life and Letters of Charles Darwin, D. Appleton and Co., New York, 1911, Vol. 1, p. 39.)
During his theology studies he wrote, I do not think I hardly ever admired a book more than Paley's 'Natural Theology.' I could almost formerly have said it by heart. (to John Lubbock, 15 November, 1859) and so pure and holy a comfort as the Bible affords, compared with how useless the sympathy of all friends must appear. (to D. Fox, 23 April, 1829).
Darwin cut short his theological studies to join the HMS Beagle as an unpaid naturalist with the official position of "Gentleman Companion" to the captain (a deeply religious man who believed every word in the Bible ), and for the next five years Darwin heard the Bible read and expounded on a regular basis. Darwin remembers his own religious orthodoxy, writing of a discussion with some of the Beagle's Officers, to whose amusement Darwin quoted the Bible as, an unanswerable authority on some point of morality.(Life and Letters of Charles Darwin, D. Appleton and Co., New York, 1911, Vol. 1, p. 277).
In 1844 Dawin wrote to his friend Joseph Hooker concerning the immutability of species. This shows that his thinking was way outside of the conventional accepted religious views of his day. He went on to discuss the idea in Origin of Species, "Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists until recently entertained, and which I formerly entertained-namely, that each species has been independently created-is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the most important, but not the exclusive, means of modification."
In his autobiographical "Recollections of the Development of my Mind and Character," prepared during the summer or 1876, we have one of our best sources. Darwin wrote, I had gradually come by this time, (referring here to the period from 1836 to 1839) to see that the Old Testament was no more to be trusted than the sacred books of the Hindoos or the beliefs of any barbarian." But, in deference to his mother's wishes, Darwin's son Francis, removed this and several other several passages about Darwin's critical views concerning God and Christianity, and then published the work in 1887, five years after Darwin's death.
The omitted passages were later restored by Darwin's granddaughter Nora Barlow in a 1958 edition that commemorated the 100th anniversary of the publication of The Origin of Species.
Darwin also clearly rejected the idea of religious miracles: "the more we know of the fixed laws of nature, the more incredible do miracles become"; and disparaged the recorders of the bible,"the men of that time were ignorant and credulous to a degree almost incomprehensible to us"; and often pointed out that the Gospels were wrong: "the Gospels cannot be proved to have been written simultaneously with the events"; "they differ in many important details, far too important, as it seemed to me, to be admitted as the usual inaccuracies of eye-witnesses."
Darwin, himself, summed it all up with, by such reflections as these... I gradually came to disbelieve in Christianity as a divine revelation. That does not sound like belief to me.
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