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Why they’re not better… What they’re good for

In case you’ve lived on the Dark Side of the moon for the past few years, here’s a “news” flash: the Legal Genealogist is not a fan of ethnicity estimates.

Those percentages reported by the DNA testing companies — x percent Irish and y percent Scandinavian — are not scientifically valid representations of our exact ethnic heritage.

I’ve said this before.

Others have, too.

Now, read this post, by a an expert in population genetics, if you want to understand more about why these percentages aren’t better … and what they really might help tell us, if we understand their limits.

Dr. Joe Pickrell is a Junior Group Leader and Core Member at the New York Genome Center, and an Adjunct Assistant Professor in the Department of Biological Sciences at Columbia University. He has a PhD in human genetics from the University of Chicago and a BS in biology from the University of North Carolina-Chapel Hill. He’s also a co-founder of the new research website DNA.Land, and he’s the author of the blog post I want you to read.

And if you read nothing else, read this part:

…what you would ideally like to have is a detailed list of your ancestors at different time depths, each labeled with their geographic location and any ethnic self-identifiers. You could then say, for example, that 100 years ago 25% of your ancestors lived in Illinois and identified as Jewish, while 500 years ago 5% of your ancestors lived in present-day Andalucia and identified as Muslim.

Unfortunately genetic tests are about as useful as Ouija boards for obtaining much of this information, so we’re going to have to compromise with some dramatic approximations. Specifically, the approach taken by all of the commercial companies (and that we take as well) is to try to estimate the general geographic regions where your ancestors lived (and in a select small number of cases their ethnic identifiers) some indeterminate time in that past, probably something like a few hundred years ago.

Does this all sound a bit vague? It should because it is. The precision suggested by these reports is an illusion–there’s plenty of wiggle room in the definition of “general geographic regions” and “some indeterminate time in the past” to allow for very different interpretations.

Compromise. Estimate. Wiggle room.

NOT precise scientific analysis.

Estimates, not real percentages.

Not useless, since there are some things you can do even with these generalized data points. But not, not, NOT precise numbers.

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