Ralph is generally regarded as a symbol of leadership, organization, and authority on the island, but he's far from perfect. In fact, from the beginning, it's clear that his tendency is usually to go along with the mentality of the group—as seen when he joins the other boys in mocking Piggy.
By chapter 5, Ralph's appearance is beginning to reflect a lessening sense of civilization:
This wind pressed his grey shirt against his chest so that he noticed—in this new mood of comprehension—how the folds were stiff like cardboard, and unpleasant; noticed too how the frayed edges of his shorts were making an uncomfortable, pink area on the front of his thighs. With a convulsion of the mind, Ralph discovered dirt and decay, understood how much he disliked perpetually flicking the tangled hair out of his eyes...
The island is affecting Ralph physically, and his increasingly savage appearance mirrors the changes taking place in his personality. As he physically begins to blend in to the wildness of the island, he also has moments where his leadership lapses.
These changes in Ralph become apparent when the group decides to enjoy a "game" with Robert after they attempt to spear a pig. Robert becomes their pretend pig, and Ralph, who has found the exhilaration of a pig hunt unexpectedly exciting, turns this violent energy toward Robert:
The circle moved in and round. Robert squealed in mock terror, then real pain.
“Ow! Stop it! You’re hurting!”
The butt end of a spear fell on his back as he blundered among them.
They got his arms and legs. Ralph, carried away by a sudden thick excitement, grabbed Eric’s spear and jabbed at Robert with it.
“Kill him! Kill him!”
Although this is just a game, this is the first real sign of Ralph's descent into savagery. This transformation culminates in violence when, in chapter 9, Ralph and the other boys turn on the innocent Simon in a frenzy and kill him, somehow unable to even see Simon as a human being. In that moment, Ralph is so caught up in the lust for death and blood that he never attempts to save his faithful friend.