A theme is the universal meaning in the story. Each of these stories explores the dark side of human nature, and they can be each seen as a fight between the forces of good and evil.
First of all, one theme in both stories is that human nature has a dark side. Humans are not always the most wonderful of beings. Each of us has the capacity for evil within us, and then we come to a point where we have to make a choice.
“Life is for the strong, to be lived by the strong, and, if needs be, taken by the strong.” –General Zaroff
Rainsford had to choose whether it was acceptable to him to hunt human beings, despite General Zaroff’s insistence that there was nothing special about them.
The weak of the world were put here to give the strong pleasure. I am strong. Why should I not use my gift? If I wish to hunt, why should I not? I hunt the scum of the earth…
Rainsford retorts that his experiences in war did not make him “condone cold-blooded murder.” Zaroff thinks his views are old-fashioned. It is clear where this was going. Rainsford could have played along, and avoided being the hunted by becoming a hunter. If he had accepted Zaroff as a comrade, called him brilliant, and asked when he could start, it would have been much easier. Instead, Rainsford acted according to his conscience.
This same choice had to be made by Ralph and the other boys. Jack decided he wanted to be a hunter, a savage. This included not just killing animals, but eventually people as well.
Consider the description of Jack as a hunter. There is no humanity in it. He is no different than a savage, or an animal.
Beside the pool his sinewy body held up a mask that drew their eyes and appalled them. He began to dance and his laughter became a bloodthirsty snarling. (ch 4)
Jack has succumbed to his inner savage. He leads the boys to destruction, both of the island and of each other.
[Piggy’s voice was] shrilled again. “Coming in the dark—he hadn’t no business crawling like that out of the dark. He was batty. He asked for it.” He gesticulated widely again. “It was an accident.” (ch 9)
These are stories of good versus evil, passion and sacrifice, savagery and civilization.