Some of the characteristics that define Naturalism in literature are
- the power and indifference of nature;
- the determining quality of heredity and environment;
- the elimination of any option of free will.
The forceful influence of society intervenes in naturalistic stories to the extent that
- society is considered humans' natural habitat, their natural environment,
and environment is one of the two forcefully influencing factors on human behavior and psychology; the other, as stated, is heredity.
All of these characteristics are present in Steinbeck's "Flight." Pepe's struggle to survive in nature despite injuries and pursuit clearly illustrates the definitive characteristic of the power and indifference of nature while the the environment clearly determines much of what happens to Pepe as, for instance, the lion symbolizes the determinism that eliminates options fof free will that might redirect the inevitability of nature's and heredity's forces.
The trail dropped quickly, staggering among broken rock. At the bottom of the slope there was a dark crease, thick with brush, ... behind the flat another mountain rose, desolate with dead rocks and starving little black bushes.
his head jerked up. ... His eyes were slits of weariness. Twenty feet away in the heavy brush a big tawny mountain lion stood looking at him. Its long thick tall waved gracefully; its ears were erect with interest, not laid back dangerously.
The environmental influence of society--humans' natural environment--is clearly seen in the incident Pepe is involved in town. Incidentally, a naturalistic writer would never write (as I almost wrote) "the incident that Pepe allowed himself to be drawn into" since "allowing" and "drawn into" both imply free will, which is the antithesis of naturalistic determinism.
As he talked, Mama's face grew stern, and it seemed to grow more lean. Pepe finished. I am a man now, Mama. The man said names to me I could not allow."
Mama nodded. "Yes, thou art a man, my poor little Pepe. Thou art a man. I have seen it coming on thee. I have watched you throwing the knife into the post, and I have been afraid."