A movement in fiction begun in France in the second half of the 19th century in response to the "subjectivism and imaginative escapism that seemed to characterize the romantic school." Naturalist writers were influenced by Darwinism and economic determinism. The movement sought to depict society and individuals as objectively and truthfully as possible.
Characterized by a "detached method of narration, meticulous accuracy of detail, and scholarly care in the documentation of historical background." Characters are often drawn from the lower class and attention is focused on their often unhappy lives.
"Emphasis was placed on the social environment of the characters and on the totally subordinate relation of the individual human being to it. In the naturalistic novel, there is a pervading sense of the control exerted over the characters by impersonal social, economic, and biological forces."
Naturalism in America was largely an "outgrowth of realism" and authors who wrote in this vein include Stephen Crane, Theodore Dreiser and Jack London.
Information is from Benet's Reader's Encyclopedia: Third Edition