When the fire burns low or goes out, we realize that the boys have lost sight of their desire to be rescued and have accepted their savage lives on the island.
The signal fire thus functions as a kind of measurement of the strength of the civilized instinct remaining on the island.
The boys’ behavior is what brings the beast into existence, so the more savagely the boys act, the more real the beast seems to become.
The Lord of the Flies is the bloody, severed sow’s head that Jack impales on a stake in the forest glade as an offering to the beast.
Later, the other boys ignore Ralph and throw stones at him when he attempts to blow the conch in Jack’s camp.
The boulder that Roger rolls onto Piggy also crushes the conch shell, signifying the demise of the civilized instinct among almost all the boys on the island.
Lord of the Flies is an allegorical novel, and many of its characters signify important ideas or themes.
Ralph represents order, leadership, and civilization. Piggy represents the scientific and intellectual aspects of civilization.
Ironically, at the end of the novel, a fire finally summons a ship to the island, but not the signal fire.
Instead, it is the fire of savagery—the forest fire Jack’s gang starts as part of his quest to hunt and kill Ralph.