In Lord of the Flies, what quotations about the conch, the sow's head, and the beast illustrate the descent into savagery?

The breaking of the conch, reverence for the beast, and the new symbol of the sow's head mark the descent of the boys into savagery. When Simon, hidden in his thicket, beholds the sow's head on a stick, its eyes "assured Simon that everything was a bad business." The fact that Jack wants to leave the head as a gift for the beast suggests the boys are falling into a superstitious, uncivilized way of thinking....

The breaking of the conch, reverence for the beast, and the new symbol of the sow's head mark the descent of the boys into savagery. When Simon, hidden in his thicket, beholds the sow's head on a stick, its eyes "assured Simon that everything was a bad business." The fact that Jack wants to leave the head as a gift for the beast suggests the boys are falling into a superstitious, uncivilized way of thinking. Simon notices that the head is

"grinning amusedly in the strange daylight, ignoring the flies, the spilled guts, even the indignity of being spiked on a stick."

Things that should have been disgusting were now acceptable, foreshadowing the depths of depravity into which the boys will plunge when they murder Simon.

After Simon's death, Jack tells his tribe that it was the beast that crawled onto the beach. He denies that they killed it, but then "a theological speculation presented itself." Jack decides they must now "keep on the right side" of the beast and "give it the head if you go hunting." Jack is creating a new religion for his tribe based on animal sacrifice to a mythical beast. This shows they are leaving the morality of the religion that informed the civilization in which they had been raised for a new religion consistent with their new savage culture.

When Ralph hides from Jack after Piggy's death, he knows that Jack will never leave him alone. He finds that

"the breaking of the conch and the deaths of Piggy and Simon lay over the island like a vapor. These painted savages would go further and further."

Later he realizes Samneric are stalking him, and he mourns that "Samneric were savages like the rest; Piggy was dead, and the conch smashed to powder." Golding links the smashing of the conch with the full-blown savagery that the boys have now entered into. 

The sow's head on the stick, offered as a sacrifice to the beast, is the emblem of the new, savage society, just as the conch was the emblem of the old, civilized one.