Select Page

As much as DNA can help…

As much as The Legal Genealogist is a total DNA geek, and as much as DNA must be considered whenever any of us sits down to map out a research plan, we are going to be disappointed if we delude ourselves into thinking that DNA is always going to help us get to an answer.

It’s simply not a magic bullet.

josiasThat lesson was drummed home again yesterday when I was privileged to attend a chat session of serious genealogists who study articles published in the National Genealogical Society Quarterly and then discuss them — what worked, what didn’t, and how things might have been better.

The article that was yesterday’s focus was mine: “‘Don’t Stop There!’ Connecting Josias Baker to His Burke County, North Carolina, Parents,” NGSQ 99 (March 2011): 25-41.

A family Bible in the possession of descendants in Texas had said that Josias Baker was born 1 April 1787, and in 1815 he had married Nancy Parks, born 20 August 1791.1 And it recorded his and Nancy’s deaths in 1871 and 1878.2

Both Josias and Nancy left wills — Josias in Ellis County, Texas (he actually died in 1870, not 1871)3 and Nancy in Dallas County.4

But neither the Bible nor the probate files — nor anything in the family’s possession, for that matter — had given any hint to Josias’ parents. Where had the Bakers come from?

In that article more than five years ago, DNA wasn’t used at all. And the question came up yesterday: if I had to do it all over again today, would I use DNA today?

And the answer is the same: no, I wouldn’t.

Here’s why.

First of all, the Bible record noted that Josias had seven children, including two sons — both of whom had died young without marrying or leaving children of their own.5 That means that the easiest way of tracing Josias back to a family of origin — a YDNA test to try to find others in the very large and very active Baker surname project that he might match — can’t be used. There are no direct male descendants to test.

As to autosomal testing, it wasn’t used at the time because it wasn’t available at all when the research was completed — the article had first been written in 2009-2010 — and not widely available even when it was published in 2011. The first autosomal tests from 23andMe weren’t available at all until late in 20096 and the Family Finder from Family Tree DNA not until early 2010.7

And today, the question would be whether DNA testing could really help move the research further towards the goalposts. As one chat participant who’s truly a DNA expert put it, testing at that level would be “crazy, difficult and expensive.”

The reason for that is that the very small handful of known living descendants of the candidate identified for Josias’ father, Henry Baker, would be — at best — fifth cousins to any of the very small handful of Josias’ known living descendants. And because of the random mixing of autosomal DNA down the generations, fifth cousins share, on average, only about three centimorgans of DNA in common with each other — about 0.0488% of their total autosomal DNA.8

That average is well below the matching threshhold for any of the DNA testing companies,9 and as a result the vast majority of actual documented paper-trail fifth cousins will not share enough autosomal DNA to be detected by the kinds of tests we use for genetic genealogy. The odds projected by the testing companies are that no more than 10% of fifth cousins will have inherited enough autosomal DNA in common to show up as a match.10

So we could test a half-dozen different paper-trail fifth cousins — or more! — against known descendants of Josias — and still come up with no match.

That’s why, at that level, we say that DNA can help provide evidence to prove a family tie — but can’t disprove it. Because the reason why you’re not getting a match may well not be because you’re not related; it may simply be because you didn’t randomly inherit enough DNA in common with your relatives to show the relationship.

In short, here five years down the road, I still wouldn’t do anything differently, even with my natural bias towards DNA testing. I wouldn’t turn down testing as an option, and I’d certainly encourage anyone interested to get tested. Considering, in every case, whether DNA testing can help is always going to be part of the planning process.

But when testing is “crazy, difficult and expensive,” and the case can be made without it, then DNA testing isn’t going to be an essential part of the reasonably exhaustive research we conduct to meet the Genealogical Proof Standard.11

DNA isn’t a magic bullet.

The word “reasonably” is there in the Genealogical Proof Standard for a reason.12


  1. Baker family Bible record, 1787–1878; The Holy Bible (Philadelphia: Jesper Harding, 1846), births and marriages columns; Bible Records Collection; Dallas Public Library, Dallas, Tex.
  2. Ibid., deaths column.
  3. Ellis Co., Tex., Will Book A:132–34, Josias Baker; County Clerk, Waxahachie; FHL microfilm 1034623, item 4.
  4. Dallas Co., Tex., probate cases, miscellaneous probate packet no. 769, Nancy Baker (1879); County Court, Dallas; microfilm 35, Dallas Public Library.
  5. Baker family Bible record, deaths column.
  6. See ISOGG Wiki (, “DNA Relatives,” rev. 25 Jan 2015.
  7. Ibid., “Family Finder,” rev. 8 July 2016.
  8. Ibid., “Autosomal DNA statistics,” rev. 25 Aug 2016.
  9. Ibid., “Autosomal DNA match thresholds,” rev. 4 June 2016.
  10. See e.g. “What is the probability that my relative and I share enough DNA for Family Finder to detect?,” Family Tree DNA Learning Center BETA ( : accessed 18 Oct 2016).
  11. See Board for Certification of Genealogists, Genealogy Standards (Nashville, Tenn. : Ancestry, 2014), 1.
  12. See Judy G. Russell, “DNA and the Reasonably Exhaustive Search,” OnBoard 20 (January 2014): 1–2, 7; HTML version, ( : accessed 18 Oct 2016).
Print Friendly