From the beginning of the story, Ralph struggles with keeping order and civility with no adults present on the island. Most eventually succumb to savagery and those who remained with the civilized ways were dealt with one way or another.
Man's instinctual Evil
It is suggested that we, as humans, are born naturally evil or animalistic and society is what makes humans more tolerable. As soon society broke down, most of the boys reverted to their primal and wicked state.
Loss of innocence
The boys on the island experience things that children do not often see or do. The events get progressively worse as the story goes on. An example of this is that at the beginning, the boys struggled to kill a piglet and by the end, they have witness or been a part of two murders and one attempted.