Why do I give a flying leap what Isaac Newton thought about the Baptists? He was a scientist, not a theologian or church historian. The aura surrounding Newton extends only to physics and calculus; on theology, Newton speaks as a layman with no particular expertise.
The simple fact of the matter is that the Baptists are derived from the Anabaptists, to be sure, but the Anabaptists didn't exist until after the Reformation. We even know the names of their leaders - Menno Simmons (i.e., the Mennonites).
I believe that Full Court might be familiar with "The Trail of Blood"....a baptist pamphlet that attempts to take their history from today back to the time of Jesus.
There are many who have disputed the accuracy of that history.
Origins
There are several views about the origins of Baptists within the Baptist church.
Separatist
This view suggests that Baptists were originally separatists in the Puritan reaction to perceived corruptions in the Church of England in the 1600s. In 1609, John Smyth led a group of separatists to the Netherlands to start the General Baptist church with an Arminian theology. In 1616, Henry Jacob led a group of Puritans in England with a Calvinist theology to form a congregational church that would eventually become the Particular Baptists in 1638 under John Spilsbury. Both groups had members who sailed to America as pilgrims to avoid religious persecution in England and Europe and who started Baptist churches in the early colonies. The Particular and General Baptists would disagree over Arminianism and Calvinism until the formation of the Baptist Union of Great Britain in the 1800s under Andrew Fuller and William Carey for the purpose of missions. American Baptists soon followed suit.
This is the most common view held by modern Baptists, which is found represented in the works of H. Leon McBeth and many others.
Landmarkist
Landmarkism is the belief that Baptist churches and traditions have preceded the Catholic Church and have been around since the time of John the Baptist and Christ. Proponents believe that Baptist traditions have been passed down through a succession of visible congregations of Christians that were Baptist in doctrine and practice, but not necessarily in name. This view is theologically based on Matthew 16:18 , "...and upon this rock I will build my church; and the gates of hell shall not prevail against it." and a rejection of Catholicism as part of the historical origins of Baptists.
This lineage grants Baptist churches the status of being unstained and separate from what they see as the corruptions of Catholicism and other denominations. It also allows for the view that Baptists predate the Catholic church and is therefore not part of the Reformation or the Protestant movement. Alexander Campbell of the Restoration Movement was a strong promoter of this idea.
J. M. Carroll's The Trail of Blood, written in 1931, is commonly presented to defend this origin's view. Several groups considered to be part of this Baptist succession were groups persecuted by the Roman Catholic Church throughout history including Montanists, Novatianists, Donatists, Paulicians, Albigensians, Catharists, Waldenses, and Anabaptists. While some of these groups shared a few theological positions with current Baptists, many held positions that would now be considered heretical by current Baptists. It is also difficult to show historical connections between those groups which were often separated by large gaps in geography and time.
The works of John T. Christian offer the best presentation of this viewpoint.
Anabaptist
Anabaptists (Mennonites, Amish, Hutterites) were a group in the 1500s that rejected infant baptism and "baptized" members as adults. They share many teachings of the early Baptists, such as the believer's baptism and religious freedom and were probably influential in the development of many Baptist characteristics. While their names suggest some connection, some Anabaptists differed from the Baptists on many other issues such as pacifism and the communal sharing of material goods.
It is difficult to say how much influence the Anabaptists had on the actual formation of Baptist churches. One of the strongest relationships between the two groups happened when John Smyth's General Baptists attempted but failed to merge with the Mennonites.
The works of William Roscoe Estep offer the best presentation of this viewpoint. http://en.wikipedia.org/wiki/Baptist