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DNA and the GPS

Alphabet soup

It’s a question that leaves The Legal Genealogist utterly baffled.

Yet we hear it all the time.

DNA.standardsFrom individuals looking at what they see as brick walls in their own genealogy.

From researchers looking at family history mysteries.

Even from students excitedly leaving the first-ever week-long institute-level courses in DNA.

“Can it be,” the question goes, that “DNA is part of the Genealogical Proof Standard’s first element: the requirement of a reasonably exhaustive search?”

Everybody agrees — or at least seems to agree — that DNA is mainstream now. That it’s a cool tool for resolving issues of proof and relationship that can’t be solved in any other way.

It’s so very much a part of our genealogical thinking now that an entire room full of genealogists watching the Cynthia Nixon episode of Who Do You Think You Are? in the common room of the Genealogical Research Institute of Pittsburgh 10 days ago all spoke up when Nixon wondered who the father of the baby born in prison might have been: “Do some DNA testing!”1

But they just aren’t quite sure — aren’t quite ready to say — that it should be part of a research plan to conduct a reasonably exhaustive search. That it’s part of the GPS.

Um… why wouldn’t it be?

Let’s start by making sure we all understand just what the GPS — the Genealogical Proof Standard — genealogy’s best practices that we all aspire to follow — means by a reasonably exhaustive search.

That GPS element calls for a reasonable effort to identify and examine “a wide range of high quality sources” in order to minimize “the probability that undiscovered evidence will overturn a too-hasty conclusion.”2

We want our research to be thorough, and that means we try to “gather all reliable information potentially relevant to the research question, including evidence items conflicting or consistent with other evidence items. Thorough research, therefore, aims to consult all potentially relevant sources. It emphasizes original records containing primary information, which may be used as direct, indirect, or negative evidence.”3

But there’s a reason why the standard is called a reasonably exhaustive search, not just an exhaustive search. The simple fact is that there is “a nearly infinite number of genealogical sources” and looking at them all is, to put it mildly, “impractical. … Convenience, expertise, financing, location, or practical concerns may limit (a research) plan’s scope.”4

So… is DNA testing the kind of “high quality source” that could keep us from making a “too-hasty conclusion”? You betcha. And that’s why we need to consider it, each and every time we are putting together a research plan to try to solve a genealogical question.

But it doesn’t mean we can use it in every single case.

First and foremost, there are some occasions when DNA just isn’t going to give us the answer we need.

Say I want to know for sure if I descend from the William Pettypool who lived in St. Mary’s County, Maryland, in the late 1600s. I can’t get the answer from YDNA testing because that sort of DNA only passes down the male line.5 Not only am I a female but I descend from a Pettypool female many generations ago, so I can’t even ask brothers or close cousins to test.

I can’t get the answer from mitochondrial DNA because that gives me my mother’s mother’s mother’s info6… so even if I had a direct unbroken female Pettypool line, it will never connect me directly to William himself.

And autosomal DNA generally can’t give you a reliable answer to a relationship question back more than five or six generations7 — and William would be my 9th great grandfather. That’s way too far back to be answered reliably with autosomal DNA.

The GPS with its reasonably exhaustive search element doesn’t require me to do something that isn’t likely to produce a reliable answer.

Second, even if I could positively identify a male cousin somewhere in my Pettypool line and a male descendant of William who might be able to answer the question with YDNA testing, one or both of those men might not be willing to test. We’ve all encountered cases where the one person we really really need to agree to DNA testing to get a question answered is the one person who is convinced that DNA testing is a communist plot.

The GPS with its reasonably exhaustive search element doesn’t require me to violate the law or ethics and steal DNA samples a cousin or test candidate isn’t willing to give.

And, of course, even if everybody involved is perfectly willing to do all kinds of DNA testing, the results often won’t give us a definitive answer anyway. Even if my documented male Pettypool cousin matched a documented descendant of William, it wouldn’t tell me that I descend from William: my line could be from a brother or cousin or uncle of William. DNA only works with the paper trail research, not instead of it.

The bottom line here is straightforward: DNA is exactly like every other kind of evidence we use in genealogical research.

Every time we consider a research question, we think about what we might look at to answer it. If I want to nail my ancestor’s feet to the floor in a particular place and time, I’d look at deeds and probate records and tax records and court records. The kinds of things that will document his or her presence when and where I think he or she was — or should have been.

But for that kind of research question, DNA testing probably isn’t going to be in my research plan. It’s not the kind of high quality source that’s likely to give me the answer I need for that particular issue.

On the other hand, if I want to know if two Smith lines in Rowan County, North Carolina, are related, then of course I’d consider DNA testing, and try to find male candidates from both lines who were willing to test.

In other words, if DNA testing is available and it’s going to contribute to a reliable answer to our research question, then why wouldn’t we do it as part of our reasonable exhaustive search?

And if it isn’t available or it won’t help answer the question, then … sigh … we’re back to plowing through all the other types of evidence we might find that will.


  1. It really was odd that they didn’t use it in that episode, wasn’t it? Can’t help but wonder if the baby Sarah left no descendants, or the descendants weren’t willing to test, or…?
  2. Board for Certification of Genealogists, “The Genealogical Proof Standard” ( : accessed 2 August 2014)
  3. Board for Certification of Genealogists, Genealogy Standards, 50th Anniversary ed. (Nashville, Tenn. : Ancestry, 2014), 14, Standard 17.
  4. Thomas W. Jones, “When Enough is Enough: How Much Searching is ‘Reasonably Exhaustive?'” Association of Professional Genealogists Quarterly 25 (March 2010): 25-33.
  5. ISOGG Wiki (, “Y chromosome DNA tests,” rev. 5 March 2014.
  6. ISOGG Wiki (, “Mitochondrial DNA tests,” rev. 9 July 2014.
  7. See generally Judy G. Russell, “Autosomal DNA testing,” National Genealogical Society Magazine, October-December 2011, 38-43.
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