Figuring out what Charles Darwin’s religious views actually were is immensely difficult, and this for several reasons. First, they appear to have changed; second, he was loathe to offend religious people; third, he was not above appearing to be religious so that he could advance his theory of evolution; and fourth, he was disingenuous.
The best place to begin is not with Charles himself, but his family. Going back two generations, we find the famous physician-poet-philosopher Erasmus Darwin, Charles’ very famous grandfather. Erasmus was the consummate Enlightenment skeptic. As far as belief in God goes, he went far beyond the fashionable Deism or Unitarianism of the intelligentsia, and bordered on atheism. He did add a whiff of theism to his evolutionary treatise, the Zoonomia (1794-1796), but that was a kind of sop thrown to believers to make his theory seem less radical. Robert Darwin, Erasmus’ son and Charles’ father, was also an evolutionist (or transmutationist, as it was called), and almost certainly an atheist.
But what about Charles? His views may have changed, but for at least the second half of his life, he was—for all practical purposes—an atheist. Anyone doubting that must read the detailed accounts of his life in Adrian Desmond and James Moore, Darwin and Janet Browne’s two-volume, Charles Darwin. Darwin did refer to himself as an "agnostic" rather than an "atheist." However, his preference for the term "agnostic" seems to have been dictated primarily by his worries about offending people unnecessarily. Sorry, folks. There’s no deathbed conversion.
The real question is not whether Darwin lost his belief in God, but when. As is well known, Darwin went to Cambridge as preparation for becoming an Anglican priest. In his Autobiography, he claims that when his father set before him the prospect of becoming an Anglican priest, Charles asked for time to think it over, being somewhat worried about having to declare his allegiance to “all the dogmas of the Church of England,” especially since, following upon two generations of freethinkers, he wasn’t all that familiar with them. So he read a few theology books, 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.”
One can hardly take Darwin at his word here. The Darwins were liberal Whigs, three-generation religious skeptics, and heirs to the Enlightenment acid critique of scriptural literalism and dogmatic belief. That Charles would suddenly have become a devout Anglican and biblical literalist, against his entire upbringing, is quite difficult to believe.
Charles did, I believe, have a kind of blush of theism while at Cambridge, given his friendship with the Anglican parson-scientists John Henslow and Adam Sedgwick, and that is when the natural theologian William Paley was most attractive to him. Darwin read Paley in preparation for bachelors examinations at the beginning of 1831. Paley presented the kind of theology that Henslow and Sedgwick warmly approved, and indeed improved upon. Nature declared the glory of God in every detail.
But if Darwin was momentarily attracted to theism, it did not last. By the time he was about to marry Emma Wedgwood at the beginning of 1839, he had to confess to her that, like his own father and her father, he was an unbeliever. His father Robert had warned him not to let the womenfolk know the extent of his own belief. Darwin was too honest for that. This nearly broke Emma's heart. She wanted to be with him forever in heaven; he didn’t even believe in the existence of the soul. Darwin had already been working assiduously on his entirely materialistic account of evolution for about two years, methodically squeezing out every place where the divine might enter. That was the account he stuck to and refined all his life.
We should not be misled by Darwin’s seemingly religious language. His private letters are full of “God bless you,” “God only knows,” “I wish to God,” and so on, but these are mere expressions (sort of like Socrates saying “By Zeus!”), and not expressions of belief. They continue long after he’d shed any belief in God. Instructing his daughter Henrietta in editing his Descent of Man, he could say “Heaven only knows what you will think of the whole,” even though he’d no belief in heaven. In fact, he explicitly argued in the Descent that the existence of religion was due, not to God, but natural selection.
Nor should we be misled by a sop Darwin attached to later editions of his Origin of Species. The first edition ended with the famous flourish: “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one…” To smooth ruffled feathers, later editions read: “There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one...” Some are fooled by this sop even to this day. But what did Darwin himself say about this little addition? “I have long regretted that I truckled to public opinion & used [a] Pentateuchal term of creation, by which I really meant ‘appeared’ by some wholly unknown process.”
Even less to his credit, he was quite willing to use those who held to a theistic account of evolution, such as, for example, the Reverend Charles Kingsley as shields against the charge of atheism. In later editions of the Origen, he added Kingsley’s affirmation that in reading Darwin he learned that natural selection allowed for a nobler conception of the deity, one who “created primal forms capable of self development.” The point is not whether Kingsley’s assessment of the possibilities of theistic evolution are defensible, but that Darwin himself, even though he thought it nonsense, was willing to use it as yet another sop for those who didn’t get his real point. In the words of Darwin biographer Janet Browne, “nothing could have been further from Darwin’s intention” than Kingley’s theistic spin. “Natural selection was a phenomenon that could never be governed, or set into motion, by a Creator. Kingsley had misunderstood that the main point of Darwin’s book was to remove the Creator from nature.”
Exactly. But he wasn’t above using theists to advance a theory which he thought would, once accepted, eliminate theism. That Darwin wouldn’t let a divine foot in the door is perhaps best illustrated by his continual battle with his friends and fellow evolutionists, Charles Lyell, Alfred Russel Wallace, and Asa Gray. They were on his side, but argued that man’s moral and intellectual abilities could not be explained by natural selection. This annoyed Darwin to no end, and to prove them wrong, wrote his Descent of Man, where he argued that not only man’s moral and intellectual capacities are brought about by natural selection, but even religion itself. That was his last word on God.