How is the theme of brutality conveyed in Lord of the Flies?
When the boys find themselves on the island, Ralph and Piggy establish order with the conch. At that point, they organize into groups, each with jobs to hunt, build shelters, and keep the fire going. So, initially, they assume a civilized society and look out for each other.
The descent into a less civilized way of life begins with Jack's preoccupation with hunting, to the neglect of the fire (which is their main chance for rescue). Over time, more of the boys are lured to Jack's side of the island where the main objective is to play on the fort and hunt. At that point, the majority of the boys are only engaged in hunting and guarding the fort (cliff). They are far removed from the more civilized society they had when Ralph was the main leader. Even after Jack and his crew steal Piggy's glasses, Piggy still believes in the power of the conch, the power of behaving in moral and civilized way. He says:
“I’m going to him with this conch in my hands. I’m going to hold it out. Look, I’m goin’ to say, you’re stronger than I am and you haven’t got asthma. You can see, I’m goin’ to say, and with both eyes. But I don’t ask for my glasses back, not as a favor. I don’t ask you to be a sport, I’ll say, not because you’re strong, but because what’s right’s right. Give me my glasses, I’m going to say—you got to!”
The culmination of their descent into a brutal way of life occurs when Roger kills Piggy. Piggy tries to reason with Jack and his followers and their (Roger's) response is violence. This is the dramatic moment of brutality: when words and (Piggy's) reason are met with violence. When Piggy dies, the conch is destroyed. This is the symbolic death of civilization on the island.