Find a Genealogist
Springboard Blog
BCG Education Fund
About BCG
Contact Us
Become Certified
Certification FAQs
Genealogy's Standards
BCG Publications
Work Samples
Educational Preparation
Associate Login

Skillbuilding: DNA and the Reasonably Exhaustive Search

From OnBoard - Newsletter of the BCG
Printer Friendly

Judy G. Russell, JD, CG, CGL, “DNA and the Reasonably Exhaustive Search,” OnBoard 20 (January 2014): 1–2, 7.

“[T]here is only one way to prove kinships beyond a reasonable doubt: DNA testing. As a genealogical standard, that is hardly practical.... DNA testing … is not available for general use.” So said Helen F. M. Leary, CG, CGL, in her January 1998 OnBoard article “Evidence Revisited — DNA, POE, and GPS.”1

“In the same way we study advanced techniques on using records or laws, we must study how to use genetic genealogy as part of thorough research.” So said Debbie Parker Wayne, CG, CGL, in her September 2013 OnBoard article “Autosomal DNA and Genealogical Research.”2

What a difference. Within a few years DNA testing progressed from an outlier technology to a commonly-understood, routinely-used tool. Now even lineage societies like the Daughters of the American Revolution accept DNA evidence as part of a proof argument in a membership application.3

But, how does DNA fit with the Genealogical Proof Standard? DNA isn’t like a deed or a will or a marriage certificate that may or may not exist. We all carry evidence of our ancestry in our genes. Where is the intersection between DNA and the reasonably exhaustive search?

Answering these questions requires, first, an understanding of what a reasonably exhaustive search is—and what it is not.

A reasonably exhaustive search identifies and examines “a wide range of high quality sources” in order to minimize “the probability that undiscovered evidence will overturn a too-hasty conclusion.”4 It is intended to be thorough research. The book Genealogy Standards describes it as research that “attempts 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.”5

Judges reviewing portfolio elements that call for a reasonably exhaustive search look for research that “extends to records that might illuminate or challenge other findings; and... covers all relevant jurisdictions and all commonly used sources appropriate for the research question.”6

It is not an exhaustive search. The word “reasonably” is inserted for a reason. It is not possible to explore every avenue of research that might result in information relevant to a genealogical question. “Studying a nearly infinite number of genealogical sources … is impractical. … Convenience, expertise, financing, location, or practical concerns may limit our [research] plan’s scope.“7

Clearly, DNA test results are among the “high quality sources” that protect against too-hasty conclusions. The utility of genetic testing in resolving complex genealogical issues is acknowledged, more than once, in the new Genealogy Standards book:

  • Standard 12 notes that, in developing an appropriate research plan, the genealogist must consider a number of factors including genetic factors “that could affect the research plan and scope.”8
  • Standard 14 on the topical breadth of research plans requires that the genealogist plan to consult a wide variety of sources bearing on the research question, including DNA sources.9
  • Standard 57 requires that reports of research results include appropriate background information, which “may include concepts from … genetics…”10

These standards and the mainstream availability of DNA testing strongly suggest that DNA testing be considered as one possible source in answering a genealogical question. That DNA testing should be considered, however, does not mean that it must be used, or that research that does not use genetic testing cannot meet the GPS.

There are practical limits to using genetics. First, not every genealogical question can be answered with the help of DNA testing. Second, DNA testing often requires the cooperation of others who may not be willing. Third, DNA testing sufficiently broad in scope to help answer a question can be expensive—in some cases prohibitively so. Perhaps most importantly, DNA by itself cannot answer even the simplest genealogical question. Only with the paper-trail evidence is DNA useful.

First, DNA cannot help to answer every genealogical question. If, for example, I want to know whether I descend from a Martin Baker who was High Sheriff of New Kent County, Virginia, in the 1660s, there is no single DNA test that will contribute reliably to the answer. None of the three DNA tests available today for genealogy works in this case.

YDNA is contained within the gender-determinative Y chromosome and passed down through the male line from father to son.11 YDNA changes very little from generation to generation and so a YDNA test could be expected to connect a modern descendant to an ancestor as many generations removed as Martin would be to me.12 However, only men in a direct line of descent will share that ancestor’s YDNA.13 As a female, I don’t have YDNA and can’t take that test even if Martin had been in my direct paternal line.

Mitochondrial DNA (mtDNA) is contained within the mitochondria and passed to all children by their mother. Like YDNA, mtDNA changes very little over generations and my mtDNA should certainly be closely comparable to an individual in Martin’s generation.14 But even if Martin is my direct ancestor, I could not expect to have any of the same mtDNA as Martin would have had: my mtDNA is from my direct maternal line from my mother’s mother’s mother, and my Bakers are in my maternal grandfather’s line.

Autosomal DNA—the DNA contained in the 22 pairs of human chromosomes that are not gender-determinative—can test across genders without regard to the direct paternal line of YDNA or the direct maternal line of mtDNA.15 But unlike YDNA and mtDNA, autosomal DNA changes dramatically from generation to generation through a process called recombination.16 As a result, while there are exceptions, in general it cannot help answer a question of relationship reliably back beyond my third or fourth great grandparents. Martin would be, at a minimum, my seventh or eighth great grandfather.

It might be possible in my case to find surrogate candidates for a YDNA test. That would require a documented male descendent with the surname Baker in my line and a documented male descendent with the surname Baker in the Martin Baker line. And I would need, from both of them, their cooperation with and consent to the testing—something that cannot be guaranteed and often isn’t achieved.

Finally, if both surrogate candidates are ready, willing, and able, and they match each other, the DNA results alone will not tell me whether I am descended from Martin. The results could only tell me if my Bakers and the Martin Baker descendants share a common male ancestor.17 It might be Martin; it could as easily be his brother, or uncle, or male cousin. Distinguishing among possible candidates would require a level of testing that, for anyone without the resources of Croesus, is not reasonably possible. And without the paper trail, even that level of DNA evidence by itself is inconclusive.

If one or both of my candidates refuses to test, I am in the same position as when I must construct a proof argument without the benefits of all the records I might like to have. Just as I might look to deeds when probate records do not exist, or to census records when vital records do not exist, I must find alternatives when this tool from the methodology toolbox is unavailable.

In the end, DNA evidence is exactly the same as any other form of evidence used by genealogists as part of a proof argument.18 It is not a replacement for traditional paper-trail genealogy but can be combined with it to build a solid proof argument. It is one tool to consider in each case where it is appropriate, may be helpful, and is reasonably available. Where DNA testing is not appropriate or not helpful or not reasonably available, it is no different from any other evidence that—in the context of a particular case—is outside the scope of a reasonably exhaustive search.

1 All websites were accessed 3 December 2013. Helen F. M. Leary, “Evidence Revisited —DNA, POE, and GPS,” OnBoard 4 (January 1998): 1–2.
2 Debbie Parker Wayne, “Autosomal DNA and Genealogical Research,” OnBoard 19 (September 2013): 17.
3 Lynn Young, “DNA Evidence for DAR Applications and Supplementals,” blog posted 5 October 2013, Today’s DAR (
4 “The Genealogical Proof Standard,” Board for Certification of Genealogists (
5 Board for Certification of Genealogists, Genealogy Standards (Nashville: Ancestry, 2014), Standard 17, at 14.
6 Board for Certification of Genealogists, “Rubrics for Evaluating New Applications for BCG Certification,” rev. 15 March 2012 (
7 Thomas W. Jones, “When Enough is Enough: How Much Searching is ‘Reasonably Exhaustive’?,” Association of Professional Genealogists Quarterly 25 (March 2010): 25–33, especially 26.
8 Board for Certification of Genealogists, Genealogy Standards, Standard 12, at 12.
9 Ibid., Standard 14, at 13.
10 Ibid., Standard 57, at 34–35.
11 See International Society of Genetic Genealogy, “Y chromosome DNA test,” rev. 30 October 2013, ISOGG Wiki (
12 CeCe Moore, “DNA Testing for Genealogy – Getting Started, Part One,” posted 18 July 2012, Geni Blog (
13 See AnneH, “Whose Y to Use? Paternal Ancestry for Ladies,” posted 7 May 2008, The 23andMe Blog (
14 See International Society of Genetic Genealogy, “Mitochondrial DNA tests,” rev. 8 November 2013, ISOGG Wiki (
15 See ibid., “Autosomal DNA,” rev. 27 November 2013, ISOGG Wiki ( See also “Autosomal DNA,” Sorenson Molecular Genealogy Foundation (
16 See generally Steve Handy, “Autosomal DNA Testing: Recombination,” blog posted 3 November 2012, DNA Genealogical Experiences and Tutorials (
17 Blaine Bettinger and Matt Dexter, “I Have the Results of my Genetic Genealogy Test, Now What?,” 2008 (updated), PDF, at 4 (
18 See generally Thomas W. Jones, Mastering Genealogical Proof (Arlington, Va.: National Genealogical Society, 2013), 4–5.

Judy G. Russell, JD, CG, CGL

This article was originally published in OnBoard, BCG’s educational newsletter and is protected by copyright. Individuals may download and print copies for their personal study. Educators are granted permission to provide copies to their students as long as BCG, OnBoard, and the appropriate author are credited as the source of the material. Republication elsewhere is not permitted.

Revised 30 April 2015
Editor’s note: This article appeared in OnBoard 20 (January 2014) and referenced a pre-publication, working title for Genealogy Standards. This revision corrects those references.

© Copyright 2007-2015 Board for Certification of Genealogists ®. All Rights Reserved.