Read the excerpt from The Call of the Wild below and answer the question. Buck's feet were not so compact and hard as the feet of the huskies. His had softened during the many generations since the day his last wild ancestor was tamed by a cave-dweller or river man.
The mention of the "cave-dweller" is most connected to the theme of .

laws
the value of work
civilization vs. the wild
the effect of the environment