American Naturalism is a literary movement that emerged in the late 19th century, influenced by Charles Darwin's theories of evolution and the scientific method. It emphasizes the idea that human behavior is shaped by environment, heredity, and social conditions, often portraying characters as products of their circumstances. Naturalist writers, such as Stephen Crane and Frank Norris, focused on the darker aspects of life, exploring themes of survival, determinism, and the struggle against nature. Their works often depict characters facing harsh realities, highlighting the limitations of free will and the impact of external forces on individual lives.