Naturalism:

A movement in the theater and literature of the late 19th century which sprang largely from scientific determinism. Darwinism influenced the naturalists to perceive a person's fate as the product of blind external or biological forces, chiefly hereditary and environmental.

The Harper Handbook to Literature, Second Edition

Dramatic naturalism was first theorized by Emile Zola, a French novelist and playwright. He praised the naturalistic novels of Balzac, and called for a new naturalistic style of theater. By this he meant what he called "the gradual substitution of physiological man for metaphysical man," or the depiction of humanity as controlled by science and nature rather than gods, spirits, or human free agency. The rise of science as the new creed of the nineteenth century was the most influential cultural change leading to the popularity of naturalism. As scientific discoveries shook human faith in God's design of the universe, people looked to science for certainty and for a window onto the world. Thus naturalism emphasized a kind of scientific or photographic accuracy in the depiction of human life. By replicating empirical details of environment, the artist would allow the audience a deeper understanding of the forces acting on characters.

Major figures:
Emile Zola
Major works: Naturalism in the Theatre
August Strindberg:
Major works: Miss Julie, The Father

Critics often describe naturalism as an outgrowth or extension of the rise of realism.