In Chapter 4 we see the further disintegration of any notions of a civilised form of society that has been formed by the boys. The forces of civilisation are weakened by Jack and his hunters, who are now obsessed with killing a pig. It is interesting that earlier on in the novel Jack justifies his hunting by answering that it is for the good of the group as a whole. Now he doesn't bother to do that - it is clear that bloodlust is the reason he is hunting, and his slide into savagery is represented by painting his face and leading the hunters in wild chants.
Ralph takes a stand against Jack, because Jack and his hunters were responsible for keeping the signal fire lit. However, they were too involved in their hunting that they neglected to do this, and so when Ralph and Piggy see a ship on the horizon it does not come to the island. Jack is now far more interested in savagery than in civilisation, as can be seen by his letting the signal fire go out. If we see the signal fire as a symbol of the hope of being saved from the island, his action in letting it go out becomes highliy significant. He no longer cares about getting rescued, just killing and hunting. It is noteable as well that Jack only admits responsibility after Ralph challenges him over it openly.
This chapter also introduces another theme of violence between the boys. A kind of Darwinian society is emerging where the strong can prey on the weak without fear of reprove. We see this when Jack slaps Piggy, breaking his glasses.