What do the responses to Piggy's plea to join the expedition tell us about both Jack and Ralph?

From the beginning, Ralph shows a certain amount of callousness to Piggy. When it is just the two of them, Ralph frequently ignores him and then reacts cruelly when Piggy shares the secret of his nickname with him. Ralph goes on to immediately tell everyone his nickname, which is perhaps the reason why Piggy votes for Jack as chief. Even though Ralph sees and acknowledges early on that Piggy sees things clearly, he points to his physical stature and asthma as disqualifying him for the expedition. At least Ralph's dismissal focuses on the practical when he says that Piggy is "no good on a job like this."

Jack quickly dismisses Piggy but flatly says that they don't want him. As was noticed by many of the boys, Jack is more willing to be simply mean and he shows this by saying that they don't want Piggy instead of making an excuse or pointing to a valid reason why he cannot join them.