Negative Evidence: genealogy methodology and DNA

Genetic genealogy, like documentary genealogy, can result in negative findings and negative evidence. What’s the difference? (It wasn’t that long ago that I was confused about that too!)

You start with a research question and a source. ‘Negative’ means the information you’re looking for in the source isn’t found. A negative finding doesn’t help you answer your research question. Negative evidence does. You may have to understand the context to know which one you have. Some examples, with document-source genealogy and DNA-source genealogy, may help.

 

Example 1.

Research question: who was Michael Darcy’s father?

Source: his 1878 death register entry, which has a field for parents’ names.

Context: informants for death records may not know how to answer this. The informant could be a second wife, who never knew or discussed her in-laws. Or it could be his youngest daughter, who never knew her grandparents. Or the clerk could be in the habit of leaving this field blank for adult deaths and only filling it in for the deaths of children. While a death date on a death record is pretty important and reliable, some other information—like names of parents of the deceased—may not be.

Result: the information we seek in the source is missing. No parents’ names were entered. In this example, it’s a negative finding. It doesn’t help answer the research question.

Example 2.

Research question: when did Michael Darcy’s wife Mary die?

Source: an 1868 deed in which he sold land.

Context: the law required the wife to document her agreement to the sale. This is called a dower release, and laws requiring this vary by state and time. In this case, if Michael was married, state law said his wife’s name should be on the deed. As this is a legal document, its content should be pretty reliable.

Result: the name we seek in the source is missing. This is negative evidence. The absence of his wife’s name in this example does help with the research question. Mary died before 1868.

 

The same ways to look at negative findings and negative evidence can apply to genetic genealogy.

Example 3.

Research question: is Michael Darcy the father of James Darcy?

Source: Autosomal DNA. Tester J is descended from James Darcy. Tester K is descended from Michael Darcy’s confirmed son John.

Context: If James is the son of Michael, Testers J and K would be 4th cousins to each other. Not all biological 4th cousins share enough identical DNA to be considered a match. Maybe 30-50% do not.

Result: K is not on J’s match list. This is a negative finding; it doesn’t prove they aren’t 4th cousins, and doesn’t help answer the research question.

Example 4.

Research question: is William Hammond the father of James Hammond?

Source: Y-DNA, 37 markers. Tester F is a direct male-line descendant of James Hammond. Tester G is a direct male-line descendant of William Hammond’s confirmed son John. Tester H is a direct male-line descendant of William Hammond’s confirmed son David.

Context: If James was the son of William and brother to John and David, their testing descendants would be 5th cousins to each other. They should share the same haplogroup and be on each other’s match lists.

Result: F does not have G or H on his match list. He has a different haplogroup than G and H. (G and H do match each other on haplogroup and do appear on each other’s match lists.) This is negative evidence for F; it does help answer the research question. F does not share a direct male-line ancestor with G or H in a genealogical timeframe, and it appears that F’s ancestor James Hammond is not the son of William Hammond.

Important note: evidence is an answer to a question, but that doesn’t mean it is always correct. The name of parents on a death certificate could be wrong. The birth information in a census could be wrong. A DNA conclusion could be overturned with later evidence. (For example, in the Y-DNA scenario, maybe John and David were raised by William and given his surname, but they were really the orphaned sons of William’s sister.) As genealogists, we want to do reasonably exhaustive research to collect and analyze as much evidence as possible. Then we draw conclusions, and we revisit them if new evidence emerges in the future.

In my next post, I hope to dig into the really fun stuff: negative evidence with autosomal DNA!

Ann Raymont (c) 2017

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One thought on “Negative Evidence: genealogy methodology and DNA

  1. Pingback: Negative evidence: autosomal DNA | DNAsleuth

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