Why do we take DNA tests? Reasons vary. Many people hope it will “tell me who I am.” That’s a reasonable expectation for adoptees and others with questions about their own parents and siblings. Others swab or spit because they think it will tell them where their ancestors come from. Experienced family historians turn to DNA to help resolve questions for which paper-trail research has turned up no explicit answer.
Regardless of our purpose: a successful outcome lies in those two words questions and answers.
This week, a thoughtful researcher asked how DNA testing fits into the Evidence Analysis Map that researchers have now used for 20 years. To answer that question,
- Friday’s post considered the first path of the map: sources.
- Saturday’s post considered the second path: information.
- Today, we consider the third path: evidence.
DNA tests certainly give us information. However, information and evidence are two different things. Information is the data set or words that make an assertion. Evidence is
- our interpretation of what those words or data mean; and
- our use of those words or data to solve the problem.
Whether we work with DNA or historical records, creating evidence out of information requires two things:
- We must first define the question we are trying to answer.
- We then ask whether the information is relevant to that question.
When information is relevant to our specific question, it becomes evidence for that question (but not necessarily for a different question.) That evidence may be one of three types: direct, indirect, or negative.
Evidence is direct when it directly addresses the question. That answer may be right or wrong. It seldom tells us everything we want to know. But if it directly addresses the question, it is evidence we must consider.
As an example in a DNA context:
Question: “Who is my mother?” DNA test results tell me explicitly that a mother-daughter relationship exists between me and a fellow tester, Ruthie Roe. Those words and the data that support those words are direct evidence to answer my question.
Evidence is indirect when it relates to the question in a round-about way, but it does not explicitly answer the question.
As an example in a DNA context:
Question: ”Who is my mother?” The DNA report identifies no match with that relationship. It does report that another tester, Robert Roe, shares sufficient centimorgans to be my half-brother. Does that answer the question, “Who is my mother?” No. Is it relevant to my question? Yes. It’s indirect evidence that I can combine with results of other research to determine (a) whether Robert and I share a father or a mother; and (b) who our shared parent might be.
Sherlock Holmes described this best with his observation of “the sound of the dog not barking.”1
In our research, the lack of something may or may not be negative evidence. It depends upon the situation and what is normal for that situation. So we ask: Given the circumstances, is this result an aberration? A missing record is usually not an instance of negative evidence. But when a record is found and a critical element that we “always” see in that type of record is missing, that can be negative evidence. (EE's QuickLesson 13 and QuickLesson 17 demonstrates the kind of negative evidence we can find in historical records, analyzing a baptismal record in the first case and the question of an enslaved child's parents in the second.)
In a DNA context, the issue of negative evidence is fuzzier. Some argue that negative evidence cannot exist with DNA because (a) test results are based on scientific data; and (b) a comparison between two testers either rules in or rules out the expected kinship.
That is clearly the case for some research questions. On the other hand, a different question or a different test can generate different types of evidence:
- Tester A questions what he has always been told: that his father’s father’s father’s father’s father, was “pure-blood” Native American. A Y-DNA test reports that his haplogroup is R1b1a1a2—the most-common Y-haplogroup in Europe. That test negated what the tester sought to prove, but that is not negative evidence.
- Tester B questions the truth of the family tradition that he has Native American ancestry. An autosomal test reports no NA markers for him. That might be considered negative evidence—an absence of evidence when the specific situation should produce evidence—but it is not "proof." The current state of genetic science leaves the question open. It is possible that the ancestry exists but NA markers were lost amid recombination across generations. Other questions have to be answered in order to use the DNA evidence correctly. (Even Sherlock had to consider whether there might be other explanations for the dog not barking.)
One thing is obvious: Past first-degree relationships, DNA testing does not supply quick and easy answers to “prove” a relationship. There’s much to consider. We, ourselves, develop the “proof” through our use of sources, information, and evidence. Tomorrow, we’ll look at how we can validly use these three paths of the EAM to reach a conclusion that does meet the Genealogical Proof Standard.
1. Sir Arthur Conan Doyle, The Adventures of Sherlock Holmes, Wordsworth Classics ed. with introduction and notes by Julien Wolfreys (original 1892; annotated reprint, Hertfordshire: Wordsworth, 1992), 291–307.
HOW TO CITE: Elizabeth Shown Mills, "Applying the EAM to DNA: Part 3, Evidence," blog post, QuickTips: The Blog @ Evidence Explained (https://www.evidenceexplained.org/quicktips/applying-EAM-to-DNA-part-3-evidence : posted 12 August 2018).