Read the excerpt from part 3 of The Call of the Wild. Pike, who pulled at Buck's heels, and who never put an ounce more of his weight against the breast-band than he was compelled to do, was swiftly and repeatedly shaken for loafing; and ere the first day was done he was pulling more than ever before in his life. The first night in camp, Joe, the sour one, was punished roundly—a thing that Spitz had never succeeded in doing. Buck simply smothered him by virtue of superior weight, and cut him up till he ceased snapping and began to whine for mercy.

The evidence from this excerpt best supports the theme that

strong leaders know how to maintain order.
we are all ruled by our natural instincts.
loyalty can be a strong force in the wild.
only the strongest are able to survive.