I agree with the post above. Golding's comment is a counterpoint to suggestions that "uncivilized" people are innately more savage than "civilized" people. All people, according to this novel, are equally near savagery, whether civilized or uncivilized.
In Lord of the Flies, William Golding is saying that within the human race, there is the instinct to live civilized or to follow a natural tendency to live as savages.
There is a conflict within man between civilization and savagery. This conflict can be expressed as good versus evil, or order versus chaos, or law versus anarchy.
The will to do the right thing is in conflict with the desire for power or immediate gratification. As one writer said, where there is a desire to live within the rules, evil is always present (Roman 7:21).
Truly, Golding writes about two characters who represent different ideas. Ralph, the protagonist, desires rules, discipline and order. He desires the boys to build shelter. Jack, the antagonist, represents savagery and desire for power. He brings out the hunter instinct in the boys.
Obviously, the boys are losing their sense of right and wrong. Through the hunting dance, they are worked into a frenzy and they kill Simon with their bare hands and teeth. Furthermore, Piggy dies at the hands of violence. Although Ralph has tried to keep order, he gets caught up in the violence at one point.
Golding is saying that evil is innate. While on the island, rules and restraints are cast to the wind and a violent side of the boys is the result. The boys lose their sense of innocence that they possessed at the beginning of the novel.