The movement of naturalism was greatly influenced by the 19th-century ideas of Social Darwinism, which was in turn influenced by Charles Darwin's theories on evolution. Social Darwinism applied to the human environment the evolutionary concept that natural environments alter an organism's biological makeup over time through natural selection. Social Darwinists and naturalists cited this as proof that organisms, including humans, do not have free will, but are shaped, or determined, by their environment and biology. Naturalists argued that the deterministic world is based on a series of links, each of which causes the next (for more on these causal links, see Causal links and processes, below). In "To Build a Fire," London repeatedly shows how the man does not have free will and how nature has already mapped out his fate. Indeed, both times the man has an accident, London states "it happened," as if "it" were an inevitability of nature and that the man had played no role in "it." The most important feature of this deterministic philosophy is in the amorality and lack of responsibility attached to an individual's actions (see Amorality and responsibility, below).
