DNA testing, when applied to genealogy, seems so science-y that we begin to think of it as a turnkey operation: enter facts, press button, out comes the answer.
Not so fast, I've discovered. The results of our exploration may be far more nuanced than we'd hoped. Take my quest to discover the identity of my second great-grandmother's parents. Catherine Laws and her descendants are easily traceable from their home in tiny Erwin, Tennessee, but she becomes a cypher once we try to pass beyond the sparse documentation asserting her marriage to Thomas Davis on November 6, 1856.
Of course, now I can take my research problem to my DNA matches at the four major companies where I've tested, and hope one is close enough to lead me to the answer I'm seeking. But it isn't always as straightforward as one would hope; there may be pitfalls. Gaining a clear understanding of the background information of Catherine's situation can help eliminate some false leads and steer us closer to the right direction.
Today, we'll examine just a few of the pitfalls I want to avoid, before we move on to inspect the best candidates to lead us to our answers.
When we first find Catherine Laws, it is upon the occasion of her marriage. That event took place not in the location of her birth—North Carolina, a fact we don't uncover until the 1880 census—but in Washington County, Tennessee.
Unless a researcher lives in or near the area of their ancestors, it is hard to understand how the location of the county can impact the result of research. In Catherine's case, Washington County at the time of her marriage was far larger than it was when, over two decades later, she showed up in a different county, known as Unicoi County. She may well have been living in the same place all along, with the county line moving around her, since Unicoi was actually carved from Washington County in 1875. In addition, the area which became Unicoi County borders the state line dividing Tennessee from North Carolina. With that, we realize that this woman who grew up in one state and removed to another may have accomplished that transition simply by following a road over a mountain pass.
To complicate our DNA scenario, when I look at Catherine's descendants—my great-grandfather Will Davis' collateral lines—I realize that both he and his older brother married women whose maiden names were Boothe. Granted, that can be a fairly common surname—and I have yet to find where the two women might be related. But here's the catch: these are two women living in a relatively isolated mountain area in a county which, at the time, boasted a population of less than four thousand people. There is a good chance that any descendants of those two lines might be doubly related to each other, both through their Davis line and through their Boothe line.
Fortunately, there are records showing that, for a while, Catherine and Thomas Davis may have moved to neighboring Greene County, Tennessee. But even that may interject double relatives, if the Laws families living in Greene County at the time were actually Catherine's relatives. Here's the reason: some of those Laws people married spouses by the name of Broyles—yet another surname intertwined in my roots. In fact, whether in Greene County or back in Washington and Unicoi Counties, there were plenty of Broyles family connections to complicate DNA results.
With limited populations living in small, isolated communities, the chance becomes all the greater that there may be some sort of pedigree collapse among any possible DNA matches. To help me with my current research goal of determining Catherine's parents, I'd need a DNA match—or more—to clearly demonstrate that we are related only through the Laws line. Granted, that would include an as yet unknown to me maiden name of Catherine's mother, as well. But it is important that it not mix in any connections with the Boothe or Broyles lines.
A straight across DNA match with someone else descended from Catherine's parents—my Laws third great-grandparents, whoever they were—would involve connecting with a fourth cousin. According to Blaine Bettinger's updated Shared cM Project at DNA Painter, matching fourth cousins can share as much as 139 centiMorgans—and, of course, anything less than that amount. Yet I certainly do not come anywhere as close as that highest amount, when examining potential Laws matches. Most of my Laws matches include much smaller amounts—down to numbers far below twenty, which I consider to be beyond a prudent cut-off point.
Even in the smaller amounts, hovering around the 20 cM cut-off point, I watch for one more detail: whether the match and I share multiple segments or just one. At the smaller numbers, spotting just one segment in common gives me more confidence the inherited segment came from only one family line—not splinters from the blended Boothe/Davis or Laws/Broyles scenarios I wish to avoid. In gleaning all the Laws connections I could find via AncestryDNA, that is exactly what I looked for: DNA matches with the Laws surname in their roots who, if a distant relative, only shared one segment with me. Tomorrow, we'll take a look at what I found.