Which symbol is used, at different times, both to represent the boys' connection to civilization and their innate potential for devolution and self-destruction? Why?
Piggy's specs: when whole, these represent the shining light of knowledge, but when broken or missing, they show only the boys' inner savagery.
The fire: the controlled, smoky signal fire is a representation of the boys' efforts to return home, but the wildfires they set are deadly.
The conch: when they obey the summons of this powerful symbol of authority, it shows that civilization is still in charge, but when they fail to heed it, it shows the collapse of their ability to self-govern.
The beast: fear of this supposed monster causes the boys to cling to any shred of civilization they have left, even though giving in to its darkness will be the downfall of all the boys.
The masks: these serve to cover up the boys' civilized faces and transform them into callous, primal killing machines.