Charles Darwin came from a family of skeptics and freethinkers and although at one point he studied for the clergy, it was clear that he was never that religious and his research into the origins of species frayed even that weak link and he moved away from the biblical theories of special creation that were dominant at the time and became an unbeliever as a young adult.
But during his lifetime, he was cagey about his lack of belief in god or his disassociation with Christianity. He was averse to conflict and may have felt it better to not let his personal beliefs about god create a controversy and overshadow his important scientific work. Furthermore, his wife was very devout and theirs was a loving relationship and he knew that his lack of religious faith troubled her deeply and he likely wanted to avoid the subject altogether.
But in 1880, Darwin replied frankly to a young lawyer named F. A. McDermott, who inquired about his faith and promised he would not publicize the answer. Darwin’s response was blunt:
I am sorry to have to inform you that I do not believe in the Bible as a divine revelation & therefore not in Jesus Christ as the son of God.
As the article says:
For decades Darwin had avoided publishing his ideas about evolution in order to shield his family, especially his religious wife, from any hint of scandal. On this letter to McDermott, he scrawled the word “private” across the top, a significant addition considering the provocative content. Even at the age of 71, he was wary of expressing his true thoughts about his faith. “Darwin never flaunted his disbelief, but he never denied it,” said David Quammen, author of The Reluctant Mr Darwin and editor of the illustrated edition of On the Origin of Species.
The lawyer kept his end of the bargain and the letter was not revealed for more than 100 years.
The letter, written less than two years before Darwin’s death, should settle any doubts on the matter of whether Darwin was a believer, that were fostered using the common tactic of unverifiable deathbed conversions, something that are imputed to all manner of prominent atheists.
After Darwin’s death in 1882, rumours of a deathbed conversion circulated. This letter, written less than two years before, defends against such claims.
“There has been fog and falsehood and wishful thought surrounding the subject of Darwin’s religious belief, or lack of it, for more than a century,” said Quammen. “The McDermott letter of 1880, a real historical document, reaffirms all the other genuine evidence we have about Charles Darwin’s rigorous, courageous agnosticism throughout the second half of his life.”
I doubt that this will stop religious believers though. Just as Albert Einstein’s letters, one written just a year before his death, emphatically rejecting any belief in any kind of personal god has not stopped religious people from trying to claim him as one of their own, so it will be with Darwin.