How is Naturalism different from literary realism?

Naturalism, while extending the tradition of literary realism, is distinguished by its adoption of scientific principles and a more rigorous, unselective representation of reality.12

The primary differences include:

• Scientific Determinism: Unlike realism, which focuses on objective observation and social mores, Naturalism is rooted in the assumption of scientific determinism. Naturalist authors, led by Émile Zola, viewed characters as products of heredity and environment, driven by instinctual forces rather than moral or rational choices.123
• The Role of the Author: While realists acted as observers of social life, Zola argued that the Naturalist writer should function as a detached "experimental scientist," subjecting characters to tests to demonstrate the relationship between their milieu and their behavior.31
• Perspective on Fate: Realism often maintains a sense of moral judgment or humane understanding regarding its subjects. In contrast, Naturalism presents a pessimistic view where individuals have little control over their fates, often documenting sordid or oppressive environments in "slice of life" detail without traditional moralizing.21

Ultimately, Naturalism sought to push the boundaries of realism by applying a mechanistic theory of psychology to literature.31