In Chapter 1 he is also the only one, other than Ralph, who refers to an adult relative. While Ralph refers to his father, Piggy keeps mentioning his auntie--at least four times. Piggy is the one with the knowledge as to how to blow the conch and that the conch can be used to call a meeting. He is also the voice of realism in the first chapter. He is the one who knows that the plane has crashed, and that all the grownups who came with them are dead. He knows also that they are on an island and that rescue may be a long way off.
In Chapter 2, this role is reinforced when Piggy becomes the spokesman for the littlun with the birthmark. The littlun evidently shared his fear with Piggy, and Piggy like an adult encourages him to express his fears of the "snakelike things" to the assembly. In Chapter 2, Piggy chastises the boys when they get out of control at the prospect of making a signal fire by saying that they are "acting like a bunch of kids," as if he is the adult and the rest are children.
Almost everything about Piggy's approach suggests a connection to civilization and the adult world. He is the one going around trying to find the names of all of the boys, creating a list and a record of who is there, after also suggesting that they summon all the boys together to get organized. Piggy suggests that they should have an election to determine who the real leader will be. Both of these actions, but particularly his desire to make a list of the boys and start to keep track of everyone is particularly important in linking him to the world of adults.
He is seen as a Jesus like figure, caring for the little ones and trying to bring about discipline and order while Ralph, Jack and Simon are of on their own business!
He is the most mature out of all of them.