The male Y chromosome DNA test follows the single male "surname" line ( in 
my case, my Davidson father, my Davidson grandfather, my Davidson 
great-grandfather, etc.).  As such, the test tells you NOTHING about any of 
the females in your line, nor anything about the males (with different 
surnames) that those females married (e.g, your mother's father does not 
affect the test results, no matter what his surname was).  The DNA test 
cannot tell you who the "most recent common ancestor" was between you and 
another matching/nearly matching DNA donor; it can only tell you that you 
have very high "odds" (or not) of sharing such an ancestor with that other 
donor in some reasonable "genealogically significant" timeframe (like 
roughly 600-700 years ago or less).

Despite the above "problems" with DNA, I would not take a million dollars 
for my test results.  They prove (over 99% odds within 16 "generations 
back") that I share a common male Davidson ancestor with the group of 
Davidsons that was in Goochland Co., VA (in the 1740s), and hence, with the 
Davidsons who were in James City Co., VA by at least 1682.  I had always 
suspected that I was probably connected to that Davidson family, but without 
DNA, I absolutely, positively could never have proven it (no matter how many 
trips I made to the Library of VA or to the applicable courthouses).  There 
are many "success stories" like this in our Davidson/Davison/Davisson DNA 
testing project (ditto other surnames).  DNA is just one more (very good) 
tool to help us with genealogy, so why not use it?  I simply can't imagine 
anyone serious about researching a family not taking advantage of it....if 
they can find a living male with the correct surname from the family of 
interest....and if they can afford it.  I sometimes think that some 
"genealogists" are simply afraid that the results will prove that much of 
what they have believed (and boldly stated) for the last 30 years is 
wrong....but the truth, however painful, is all any of us should really 
want.

DNA is also great at proving to whom you are NOT related.  It is great to 
eliminate the "wrong" families with the same surname, especially if the 
surname is fairly common.  I know many people who were "positive" that they 
were part of family "A" (with DAR applications to prove it), only to learn 
via DNA that they are positively not a member of that family after all.  In 
some cases, these folks matched some other donor in some other family with 
the same surname, but in other cases, these folks matched no one (so far, 
anyway).  In some cases, a person has one or more matches, but the match is 
only to some OTHER surname.  As DNA testing continues, it is becoming more 
obvious that adoptions and "affairs" were much more prevalent than most of 
us ever thought possible.

I know that Ancestry.com joined with the DNA testing company Relative 
Genetics (I don't know "who bought whom").  I will just leave it at 
this....I highly recommend Family Tree DNA for DNA testing (and no, I do not 
receive any compensation of any kind for saying that).

Bill Davidson 

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