I have seen it argued that a mysterious “Q” Gospel had to have been written prior to any of the Gospel accounts. Some scholars are a little uncomfortable with the “Q” document premise since there is absolutely no hard evidence for it, but they prefer it over a “Matthew first” position when Mark doesn’t have the miraculous birth or resurrection accounts. The presumption is that these records would have been added to a later version of the Gospel. Nevertheless, if Mark represents the transcript of a series of Peter’s sermons at Rome as 2nd and 3rd century AD witnesses inform us that it is, there would be no reason for a birth account showing genealogies etc. If one is delivering a speech or sermon, a long list of foreign names makes for very dull reading and or listening. Even the mention of the virgin birth would be out of place, unless one described its occurrence and showed how this fit into Jewish tradition and/or was important to gentile Christians. Matthew and Luke were both written for specific reasons, but Mark is described by 2nd and 3rd century witnesses as a transcript of what Peter preached at Rome. It was not intended to be a written witness to prove anything. Rather, it was simply Peter’s testimony at Rome about Jesus of what he had both seen and heard.
Some scholars would jettison the “Q” document idea in favor of the “Mark First” theory, taking note of almost exact wording of some sayings of Jesus in the Synoptic Gospels, and add to this the presumed antiquity from the lack of birth and resurrection accounts. However, concerning the reasons for no birth account I’ve submitted my argument above. As far as the resurrection account is concerned, it is true that the final 12 verses of Mark are held to be doubtful in the original, but this comes from preferring the Alexandrian witnesses of the 4th century over other witnesses. Near the end of the 3rd century Lucian of Antioch produced a Greek text that contains the disputed verses, and it became the dominant Greek NT text at that time and in later centuries. The problem is, however, it was produced prior to the Diocletain persecution of the early 4th century. At that time much of Christianity’s sacred manuscripts were seized and destroyed. Nevertheless, when Constantine came to power a few years later, the Lucian text became the preferred text of the Christian leaders in the Eastern Church (Rome used the Latin text), and it was this very text that formed the basis of the Byzantine text which Erasmus in the 16th century used to compile his “Textus Receptus.” Dr. Hort, a proponent of the Alexandrian manuscripts, even dubs Lucian as the father of the Byzantine text. So, the matter of the last twelve verses of Mark, or the resurrection account, has at least as early a history as the Alexandrian witnesses that do not contain the verses. Therefore the argument that Mark has signs of being the earliest Gospel written is largely rendered moot when we take church history into consideration.
If we consider the likelihood of Luke and Matthew containing the exact wording of some of Jesus’ sayings etc., one could see that the idea is not as strange as would at first seem. If three authors wrote about the events and sayings of a certain individual, it would be expected that many similarities would surface, but it would be unlikely that we would have exact wording in all three accounts, unless one was actually quoting the exact phrase of the person under consideration. In the Synoptic Gospels we have a common source—Peter. Mark’s Gospel is really Peter’s Gospel. Mark wrote down what Peter testified at Rome. It was the Gospel or testimony that he normally used when preaching to the various churches throughout the Roman Empire. Peter would also have had a great amount of input in Matthew’s Gospel. If Matthew kept a journal, Peter’s testimony would have been a large part of that journal. Even if Matthew did not keep a journal, Peter’s testimony would have made up a large part of whatever Matthew wrote down. Peter was the acknowledged leader of the apostles, and one of the three closest apostles to Jesus. Similarly, Luke testifies in the first four verses of his Gospel that he searched out the truth and recorded the testimony of those who knew Jesus. Peter would have had to have played a large part of Luke’s research, and a comparison of his Gospel with that of Mark would make this understanding very likely.
Therefore, a Markan priority is really not necessary. Clement of Alexandria testifies in the late 2nd or early 3rd century AD that the Gospel of Mark was a result of Peter’s sermons at Rome not long before his death in the persecution by Nero, but the Gospels with the birth accounts (Matthew and Luke) preceded his. The Gospel of John came later but the entire New Testament, according to Clement of Alexandria, was written between the reigns of Tiberius and Nero, Emperors of Rome. There is a lot we can understand about the New Testament pertaining to who wrote what and when, if we only consider the context of the particular books and the writings of the early church fathers who wrote about the things that occurred in the 1st century AD.