In the grand tradition of naturalistic literature, the narrative woven in McTeague stands in stark contrast to the liberated individual celebrated by Ralph Waldo Emerson in works like "Self Reliance" (1841). Rather than being a free agent, McTeague's protagonist is ensnared by the relentless forces of heredity, environment, and chance. These ever-present influences push the individual toward both physical and mental decline. To bring these sobering themes to life, Norris adopts a framework derived from popular interpretations of evolutionary theory, as influenced by thinkers like LeConte and Lombroso.

At the narrative's outset, McTeague, a hulking, mentally sluggish, and psychologically rudimentary figure, stands at the pinnacle of his personal evolution. His life, rooted in simplicity, is thrown into chaos when he is drawn to Trina, a girl with roots in a thrifty Swiss peasant lineage. Their ensuing courtship and marriage ignite McTeague's latent brutality and Trina's ingrained thriftiness—two deep-seated instincts that dictate their actions. Fate and circumstance then conspire to accentuate their regression to a more primitive state.

In a twist of fate, Trina strikes it rich with a five-thousand-dollar lottery win. Simultaneously, McTeague's career crumbles when Marcus, Trina's former suitor, exposes his illegal dental practice. Stripped of his livelihood, McTeague succumbs to alcoholism, while Trina's avarice intensifies. This downward spiral in their social standing mirrors their psychological unraveling, culminating in McTeague's descent into a world of crime. He murders Trina, seizes her money, and retreats to the mining territories of his origins.

Haunted by an instinctive awareness that he is being pursued, McTeague seeks refuge in the desolate expanses of Death Valley. There, Marcus finally catches up with him. The story reaches its somber conclusion in the inhospitable desert, with McTeague shackled to Marcus's lifeless body.

Beyond its deterministic framework, McTeague delves into quintessentially American themes and myths, casting them through the lens of social Darwinism and weaving them within a tapestry of the grotesque and monstrous—a hallmark of the turn-of-the-century aesthetic. McTeague's downward spiral serves as a stark inversion of the "self-made man" narrative, while Trina's tightfistedness starkly opposes the traditional American ideal that thrift is the key to social ascension. The novel's portrayal of McTeague as a miner and Marcus as a cowboy deftly punctures the romanticized myths of frontier life, challenging the optimistic dreams associated with the West's boundless promise.

Furthermore, the greed that consumes Trina, the criminality that taints McTeague, and the jealousy that gnaws at Marcus—all sparked by the gold Trina wins in a lottery—provide a sharp critique of the pervasive materialism that characterized the waning years of the nineteenth century. This narrative aligns itself as a poignant reflection on the corrosive influence of wealth and the dark undercurrents of American ambition.

The first theme, and most obvious, is that of greed. The three main characters (McTeague, Trina, and Marcus) all strive for something better in the world. None are happy with their stature in life. All three come to find out that the cliche "money is the root of all evil" is true. All three find that, in the end, money causes their downfall. Each dies as a result of the personal goal of becoming rich (defined individually). As a result of each individual's greed, the money possessed is never enough, and the search for more money is directly responsible for each of their deaths.

The second theme, the animalistic nature of mankind, is illuminated directly by the author. Numerous times throughout the novel, characters are compared to animals. For example, in the opening chapter and opening description of the protagonist, McTeague is compared to a horse: "McTeague's mind was as...

These comparisons help to highlight the final theme: natural selection. Within the comparison to a horse, Norris illuminates McTeague's "docile, obedient" nature. Horses are domesticated in order to work for mankind. Once the horse becomes old or is unable to work, it tends to be forgotten or put down. McTeague is no different. As soon as Trina wins the lottery, her husband (McTeague) is no longer of use to her. She has risen above him, and she no longer needs him to support her. She has become the stronger of the two and should, although she does not, survive on her own. Later, McTeague is compared to an elephant. These creatures seem to be docile, much like the previously mentioned horse, but this can change in a moment. This illustrates the idea of the animal that lies beneath the surface of the human. In the end, the massive elephant is able to take down most enemies, proving itself to be a dominant beast. Lastly, McTeague is compared to a bull. He and Marcus fight in Death Valley over the money McTeague took from Trina (which also illustrates the ideology behind natural selection). Both men circle one another in a literal and figurative battle to the death. The hate the men have for one another is appropriately illustrated as fighting bulls thirsting for the blood of the other.