The Howell Y-DNA Surname Project started in 2001 as a way to determine if two colonial lines of Howell in Long Island, NY shared a common ancestor. Descendants from the two groups, (Edward Howell of Buckinghamshire, England and Southampton, NY, and Richard Howell of Southold, NY) were tested. The results excluded the two lines from sharing a common ancestor.
Since that time, the project has grown to 135 members and identified 15 seperate groups of Howells that share common ancesters and DNA. The largest group is from the Virginia Colony, followed by the original project groups in NY. Although both groups came from England in the 1600's, they do not share a recent common ancestor. The majority of the Howell's tested to date have the DNA Haplogroup R1b that is most common in England and the U.S. Based on the large population of R1b in England and the U.S., the Howell Project recommends testing at least 37 markers.
To share a common ancestor, two males must have the same Haplogroup. Once the Haplogroup matches, then the markers called a Haplotype are matched to bring the time line within range of the Surname. Surnames in England was adopted about 1066AD.
The more markers tested, the better chance to see differences/mutations/changes indicating family branches. Once a DNA marker mutates into a different number, all future generations will carry that mutation. Each marker tested will have a different mutation rate. For instance marker 393 is very stable with a rate of change of only once every 33,895 years! The big unknown, when was the last change? Thus the more markers you have tested, the more likely you will see a change that helps identify your line from other more distant relatives.