Read the excerpt from The Call of the Wild. They saw him marching out of camp, but they did not see the instant and terrible transformation which took place as soon as he was within the secrecy of the forest. He no longer marched. At once he became a thing of the wild, stealing along softly, cat-footed, a passing shadow that appeared and disappeared among the shadows. He knew how to take advantage of every cover, to crawl on his belly like a snake, and like a snake to leap and strike. He could take a ptarmigan from its nest, kill a rabbit as it slept, and snap in mid air the little chipmunks fleeing a second too late for the trees. Fish, in open pools, were not too quick for him; nor were beaver, mending their dams, too wary. He killed to eat, not from wantonness; but he preferred to eat what he killed himself. So a lurking humor ran through his deeds, and it was his delight to steal upon the squirrels, and, when he all but had them, to let them go, chattering in mortal fear to the treetops.

Which theme does this passage illustrate?

A good leader is strong and intelligent and treats his followers well.
Only the strong survive in the wilderness.
The desire to fight for power is an instinct.
The only way to learn something is to try it.