… or does it?

It’s one of the most-commonly-repeated statements in genetic genealogy:

“DNA doesn’t lie.”

It’s usually coupled with: “Families do.”

And The Legal Genealogist isn’t going to take on either of those.

But — as with almost everything in genealogy — there’s more to the story.

And boy was that hammered home for me yesterday.

I’m in northern Virginia attending and speaking at the Professional Management Conference of the Association of Professional Genealogists. I gave the Friday keynote about professional ethics; Blaine T. Bettinger — who blogs as The Genetic Genealogist — gave yesterday’s keynote about using DNA evidence to prove a genealogical conclusion.

Blaine had no sooner finished his prepared remarks when a member of the audience said this one phrase — “DNA doesn’t lie” — should be eliminated from what we say as genetic genealogists, and his example was a man whose autosomal DNA did not match that of his own mother.

Now before you dismiss this as pure fiction let me assure you, the member of the audience was telling the absolute unvarnished truth: this tested man had autosomal DNA that did not match that of his own biological mother.

How is that possible?

When the person tested has had a stem cell or bone marrow transplant. The autosomal DNA in that case will match the donor — and not the donee’s own biological parent.

And Blaine himself showed an example of a case where each and every one of us, looking at the result, would have concluded that the two people tested were parent and child. The one-to-one comparison of DNA at GedMatch showed 3586.7 cM of DNA in common and a 1.0 generation difference between the two.

There isn’t a man-jack among us who wouldn’t look at that and say parent-child. And there isn’t a man-jack among us who wouldn’t have been dead wrong.

Because the two being compared were aunt and niece — the aunt happens to be an identical twin to the niece’s mother.

Powerful evidence, isn’t it?

So… should we stop saying “DNA doesn’t lie”?

No.

Because of something else that Blaine said that was even more powerful.

He reminded us that DNA alone can never be enough to prove a genealogical relationship. There’s got to be at least one more piece of information to be able to properly interpret the DNA evidence you get.

In the one-to-one comparison case, the one more piece of information we needed was that one of the people tested was an identical twin. That one more piece of information would have been enough to stop us from making the erroneous assumption that this had to be a parent-child relationship and would have clued us in to the possibility (correct in this case) that the other person tested was the twin and not the parent.

In the no-match-to-mother case, the one more piece of information we needed was that the person tested had had the stem cell transplant. That one more piece of information would have been enough to stop us from mistakenly assuming that we were dealing with a case of misattributed parentage.

No, DNA doesn’t lie.

Our interpretation can be wrong.

And in every single solitary case, bar none, without fail, we are going to need at least one more piece of information to be able to prove a genealogical relationship.

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