Robert Louis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde (1886)

Stevenson musters all possible devices, images, intonations, word patterns, and also false scents, to build up gradually a world in which the strange transformation to be described in Jekyll's own words will have the impact of satisfactory and artistic reality upon the reader -- or rather will lead to such a state of mind in which the reader will not ask himself whether this transformation is possible or not.
--Vladimir Nabokov

As the cab drew up before the address indicated, the fog lifted a little and showed him a dingy street, a gin palace, a low French eating house, a shop for the retail of penny numbers and twopenny salads, many ragged children huddled in the doorways, and many different women of many different nationalities passing out, key in hand, to have a morning glass; and the next moment of fog settled down again upon that part, as brown as umber, and cut him off from his blackguardly surroundings.  This was the home of Henry Jekyll's favourite; of a man who was heir to a quarter of a million sterling.
--Robert Louis Stevenson, The Strange Case of Dr. Jekyll and Mr. Hyde.

Stevenson's novella was published in 1886, after Darwin's On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. (1859) but before anything was published by Freud (born in 1856), whom Stevenson presages.   The novella is very different than the stage and film versions that were inspired by it, mainly because it is written as a mystery narrated by several voices, with the "solution" found in Jekyll's writing only after Jekyll is dead, poisoning himself after he can no longer keep from turning into Hyde.  The influences of Dickens and Wilkie Collins are felt in Stevenson's book, with an emphasis on the struggle between the arrogant upper classes and the impoverished lower classes, between suppressing one's instincts and giving in to them and with narrators who know Dr. Jekyll but have no idea what he is up to, with his adventures as Hyde left mostly to our imagination, except for one incident described by a narrator where Hyde tramples a young girl and pays off her parents with a check signed by Jekyll.