First, chakka... we should agree that whatever the subject, debaters on any subject, let alone one as emotionally charged as Scripture, usually come to the table with a set of biases produced by their world view (or as our German friends more accurately state "Weltanschauung". It's equally true, that most choose to consult sources which support those biases. We are no different, I suspect.
Although I willingly read the sceptics pronouncements, in the back of my mind is the niggling thought that, for each tidbit of evidence proposed by the sceptic, there exists easily accessed, thoroughly researched examples of antithesis.
Ok... as far as "development"... your example fails to demonstrate the classic definition of that term when applied to ancient documents, especailly any dealing with dogma. Primarily it fails on the basis of a disagreement as to what happened, if anything, to the ending of Mark. The original could have been lost, destroyed, changed or simply ended at v.8. Regardless, and there's serious scholarly debate supporting each, every version of Mark one may read carries the parenthetical notation that the most ancient examples of Mark do not have the following verses. That's not development of dogma or changes in the thrust or meaning of the ideas in all the Gospels. That, my interesting friend, simply has not occurred in either the Old or New Covenants.
Secondly, a premier scholar, John Warwick Montgomery, . in his extensive work "History and Christianity" ponders "...Matthew published his Gospel among the Hebrews [i.e., Jews] in their own tongue, when Peter and Paul were preaching the gospel in Rome and founding the church there. After their departure [i.e., death...], Mark, the disciple and interpreter of Peter, himself handed down to us in writing the substance of Peter's preaching. Luke, the follower of Paul, set down in a book the gospel preached by his teacher. Then John, the disciple of