What are three differences between Ralph and Jack in Lord of the Flies that also illustrate the theme of the book? What are some quotes for these differences? What are some similarities between the two, along with some quotes? What is a good thesis for comparing and contrasting the two main characters in order to illustrate the theme?

In Lord of the Flies, there are stark differences between Ralph and Jack, but unfortunately, by the end of the novel, there is one overriding similarity that far outweighs their vastly different leadership styles. They have both witnessed "the darkness of man's heart," and as "British boys," share the blame for the outcomes and particularly Piggy's death.
In considering the best way to write a compare and contrast essay that revolves around the main themes of the loss of innocence or savagery versus civilization consider the two boys' characters.
Right from the beginning, Ralph is decisive and confident, despite what must be overwhelming circumstances. His inclusive style is evident immediately as he suggests that Jack, "the boy who controlled" the choir should join the other boys who have congregated, having heard the conch. Ralph also recognizes the need for "a chief," but unlike Jack, he does not insist that he should automatically be in charge, and Ralph accepts the position based on the vote. Still Ralph is eager to show Jack some recognition, and Jack's choir is recognized as the "hunters."
Although Jack initially accepts his role, it does not take long for him to disrespect any form of order. He may hesitate the first time the opportunity to kill a pig arises, but "next time there would be no mercy," and in support of the theme of civilization versus savagery, Ralph (with Piggy's help) consistently makes plans for shelter, rescue, safety and so on whereas Jack has that "mad look in his eyes again." Jack becomes obsessed with hunting, but Ralph's main aim is rescue.
It is then tragic that despite Ralph's best efforts, he succumbs to Jack's lawlessness, and finds himself fighting for his life against "the savages." The novel ends with a glimmer of hope for future generations as there is still a civilization to go back to; otherwise the boys would not have been rescued.
On reflection, Ralph does succeed in his aims because the Navy sees the smoke, and interestingly, Ralph accepts his responsibility maintaining that he is "boss here," despite the fact that that makes him accountable for all the things he has been unable to control or prevent. Unlike Jack, who will inevitably struggle to fit back in to his former schoolboy lifestyle where he will have to conform, Ralph is also painfully aware of how changed he is, weeping "for the end of innocence."