What is the theme in McTeague: A Story of San Francisco by Frank Norris?

As befits a classic naturalistic novel, the story told in McTeague asserts that the individual, rather than being the free creature described by Ralph Waldo Emerson in such essays as "Self Reliance" (1841), is conditioned by the ineluctable forces of heredity, environment, and chance, and moreover, is at every moment subject to physical and psychic deterioration. To give these themes dramatic form, Norris follows a pattern he took from the popular interpretations of evolutionary theory he had learned from LeConte and Lombroso.