In my last post about the Amish, someone apparently misconstrued my assertion of theological kinship between Baptists and Anabaptists to constitute my advocacy of the Anabaptist Influence theory of Baptist origins. The Anabaptist Influence Theory is a respected academic theory, espoused by a number of respected historians, including the late W. R. Estep of Southwestern Baptist Theological Seminary. Historians debate the extent and timing of the influence that Anabaptists had upon the emergence of seventeenth-century Baptist congregations, but no academically published theory of Baptist origins denies the theological kinship and contact that has existed between Baptists and Anabaptists.
The debate centers around historians trying to explain the causes of the "origin" of modern Baptists.
But what does that mean? In some sense, the "origin" of Baptists is simply the willingness of people to be obedient to the scriptures. I don't believe that we can assertively identify any other "source" of Baptists as a movement.
In 1609, John Smythe and a group of likeminded believers in Holland established what became the mother church of English General Baptists. He and his congregation lived in a bakehouse owned by Dutch Anabaptists.
In the 1630s, a Baptist congregation emerged from an Independent congregation in London. This congregation became the mother congregation of the English Particular Baptists.
Also in the 1630s, Roger Williams and a group of likeminded believers in Providence, Rhode Island, formed a Baptist congregation. This congregation is not the mother congregation of all Baptist churches in the Americas, but neither is it (that we can identify) a daughter congregation of any of the English Baptist churches.
In 1753 a (roughly) Methodist congregation in Barton-in-the-Beans, Leicestershire, England, adopted Baptist sentiments, becoming one of the primary mother congregations of the New Connexion General Baptist congregations in England.
As far as the record of history reveals (or at least, as far as I know the record of history…I do not pretend omniscience even in my field), these churches were not planted by other Baptist churches and were not splits from other Baptist churches. What is the origin of Baptist churches? Well…which Baptist churches? Baptist sentiments sprung up almost spontaneously in multiple unrelated places among otherwise unrelated groups of people. The only thing they really have in common is some connection with English Separatism and a devotion to the teachings of the New Testament.
A related question asks whether Baptists existed prior to 1609. I answer that we will never know until we reach Heaven. We know for certain that dissenting groups existed throughout the Medieval period. Small, persecuted sects, worshipping in secret, trying to hide their existence from authorities, and populated by people other than the nobility—such groups deliberately left very little of a footprint. In my opinion, we can neither demonstrate the existence of medieval Baptists nor can we disprove their existence.
Again, if the origin of Baptists is obedience to the New Testament, then the question of Medieval Baptist existence really is not very important. The Roman Catholics do have an unbroken chain of existence through the Medieval period, but they are dead wrong with regard to the teachings of the New Testament. What legitimizes a church? Not its age or lineage, but its obedience to the God's Word. The churches listed above have no demonstrable earthly lineage, but their faithfulness to the teachings of the Bible give them all the lineage that they need.