Evolutionary Theology?

It is simply historically false to suggest that the intellectual boundaries of Christianity were not defined until well after the New Testament era. The evidence taht they already existed in the New Testament era is compelling. However, as offshoots and aberrations from the earlier and more apostolic faith arose in the second through fourth centuries, the church was forced to more clearly define Christological orthodoxy and orthopraxy. Then indeed the boundaries were more rigidly and firmly put in place. But this is not because before the fourth century what existed was a "free-range" Christianity that would have considered Gnosticism (or, for that matter, an inadequate Christology or polytheism or libertinism) a legitimate variant on a Christian theme. It is because the specific problems raised by such later deviations had not yet formed, or had not yet fully formed, in the New Testament era.

Ben Witherington III, What Have They Done with Jesus? (San Francisco: Harper, 2006) 224-225.