Hal --

David Carkeet's research on the flawed methodology used to establish DNA
connections to Clemens via ancestry.com family trees was the game changer.
His essay on his months long research and first hand experiences in working
with the DNA reports is online at:

http://www.twainquotes.com/Carkeet/AncestryReport.html

In a nutshell, anyone can plug in a false or inaccurate family tree at
ancestry.com after submitting a DNA test, and the ancestry.com database
will generate a list of people who are also related to people in the tree
one believes is their own tree.  Just about anyone can be distantly related
to someone else who ties in to the Clemens family tree in some fashion if
the family tree branches are traced back far enough.  From Carkeet's report:

"... 'What you are seeing is the result of endogamy, intermarriage within a
population group. In the year 1700, the population of the United States was
approximately 250,000 people.' In other words, it is a small world. Or,
more to the point, it was a small world, with so few people in the pocket
of immigrant history that I share with my matches that if I select a
specific name from the past (in this case, with my false genealogy, an
ancestor of Samuel Clemens), some match of mine from among my more than
6,000 matches will descend from that ancestor."

Barb