The connection hinges on the meanings of the word mystery, but it’s worth considering. Creation, after all, is the scene of the greatest whodunit of all time—theoretical physicists and speculative metaphysicians alike engage in perpetual forensic evidence-gathering, but they have failed to solve it conclusively.
Sir Arthur Conan Doyle’s Sherlock Holmes stories feature rational deduction solving mysteries—that is, dissolving mysteries, and revealing the machinations and human frailties that accounted for those erstwhile mysterious observed phenomena. The stories were written, and met with instant and lasting popularity, in the latter half of the 19th century, in post-Darwinian Britain. Christianity was about to enter its century of European decline; rationalism and a faith in science and technology were the hallmarks of a certain enlightened, educated Victorian mindset, and Conan Doyle himself was a doctor.
What was happening in religion was mirrored, or paralleled, in literary taste. It’s not exactly a coincidence that the first Holmes story was published in 1886, the same year Nietzsche published Beyond Good and Evil. The mystery genre, thought to have been established by Edgar Allen Poe, did not exist for most of literary history; one does not find ancient Romans or Indians or Japanese cultures reading about people solving murders, though they probably had plenty of unsolved murders back then. The mystery sprang rather mysteriously into existence in the West, in the 19th century. I suspect the ever-strengthening tendency to search for rational explanations for all phenomena (including those until then attributed to God or divine agency) has a lot to do with the popularity of the mystery genre: The supernatural hound is not really supernatural, he’s just phosphorescent. Nothing is really mysterious if you are observant enough—and it’s by observing closely (as a scientist is supposed to) and deducing the truth from his observations (again, as a scientist should) that Sherlock Holmes, beyond proving his brilliance, dispels fear and brings about justice on earth (much as a religious savior would be expected to).
But Conan Doyle’s case points to an equally interesting inverse phenomenon: That a traditional religious faith leaves a vacuum when it goes, and that something else, either silly or dangerous, usually fills its spot. The dangerous something was dictator-worship, as 20th century Europe proved, but with Conan Doyle, it was something silly: The belief in fairies and psychic phenomena. For the creator of Sherlock’s supremely rational mind was a sucker for all sorts of fake mediums and hoax seances. Dr. Conan Doyle fell for some doctored photographs of the so-called Cottingley fairies, so hard that he wrote a book about them; he argued bitterly with Harry Houdini that magic was real, even when Houdini showed him how it was all an illusion.
Why was Sherlock’s creator so stubbornly gullible? One can only speculate, not deduce, but I suspect that he wanted to believe in something supernatural, some mystery beyond the increasingly explained and explicable world—that is, the same urge to insist on the mystery of existence that drives religious minds to assert a God drove Conan Doyle to assert the existence of fairies. Technology, in this case the camera, would make the unobserved “spirit world” observable, and thereby prove it real—maintaining the promise of an afterlife. In this notion of the afterlife, the dead remain exactly as they are and appear dutifully at seances in London sitting-rooms: It was not a Christian afterlife but a “spiritualist” one, devoid of bliss and hellfire alike. In 1922, Conan Doyle defended a “spirit photographer” against the charge of trickery. The fraud’s last name was Hope.