Why doesn’t Ralph descend into savagery like the other boys on the island? How does he resist this?
Ralph, as a representation of the ego, is conscious of inner morality and guidelines. He has a strict idea of what should be done as far as leadership rituals, and he resists the other boys rejection of society's rules. He finds the conch in the beginning, and his natural confidence leads to the boys electing him leader. He recognizes the necessity to build shelters and a fire, and attempts to hold the other boys to those standards. He represents leadership by common sense and governmental authority.
This is in direct opposition to Jack's leadership through fear and violence. While Jack sees himself as a great ruler, one to be feared and obeyed, Ralph thinks of all orders in terms of what is good for the community. He doesn't care about others acknowledging his leadership, unless they go against what's good for everyone (such as refusing to build shelters or letting the signal fire go out). He also acknowledges his role in Simon’s death as murder, which shows that he has a conscience.
Despite all this, he feels the fenzy of “wounding” a boar. As hardship and tension increase, he loses the ability to think and succumbs to snarling and physical fighting. He eats the meat which Jack and the other hunters bring, and cannot stop them from harassing Piggy throughout the book. He even joins in the verbal taunting, proving that he can succumb to base impulses.
However, he & Piggy are the only ones who know the need for rescue. They struggle to keep a shaky peace, for the good of their fragile society. His meeting with the Lord of the Flies teaches him about the darkness in men's hearts, & he fights that understanding until the rescue.
In responding to this question, you can't merely say that Ralph was a good person, therefore he was not savage. It is important to keep in mind that Golding wrote Lord of the Flies to show that evil is inherent in all men. Ralph, the blond haired "good guy", is able to hold on to the civilized life he once had. He is not, though, without some evil, or savage, tendencies. He was cruel to Piggy when they first got to the island, he felt a rush of power and pride when he stabbed a pig, and - most importantly - Ralph was an active part of the savage murder of Simon. Golding uses this character to show that all people, even those who try to be "good", have evil tendencies.