Skip to content
Home » DNA kits by mail order – accuracy of determining your ancestry?

DNA kits by mail order – accuracy of determining your ancestry?

You’ve seen these advertisements on TV. Get one of these DNA kits, give them a sample of your DNA along with a few hundred to a few thousand dollars, and mail it to one of the DNA testing companies. Wait some time, and they send back information about your ancestry, potential diseases, and other information.

There seems to be a strange belief that if these DNA kits say you’re 28% German, or 37% Italian, or 13% Japanese, it speaks the truth. Anecdotally, I’ve had boatloads of friends get this test done, and they take pride in their new or confirmed ethnicity. And I won’t even go into the scares some have had from the presumptive medical diagnoses made from some genetic marker found in the result.

We’re going to focus on the ethnic testing aspect of these DNA kits. But without a doubt, there’s a lot of concern out there about those tests leading to inaccurate medical diagnoses. Many genetic diseases, like diabetes, don’t have a purely genetic cause, but generally there’s a combination of genetic and environmental basis.

23andMe, one of the leading companies in mail order DNA kits, has had a roller-coaster relationship with US FDA. After all of the back and forth, the FDA has stated that 23andMe can market their tests for genetic testing, but cannot market them as diagnostic tests. I’m not sure the public will see the difference in that.

However, I’m going to focus on what bothers me about these tests – they are becoming the basis of some kind of scientific racism. We are highlighting, and sometimes misrepresenting, patterns of differences in human species by a sampling of genes.

Let’s take a look at these DNA kits – how they do the testing. How they determine these racial/ethnical characterization. And how one should interpret the results.

DNA kits – how do they do the testing

The first thing we need to make clear right up front is that none of the DNA kits by mail test 100% of your DNA. They actually look at a tiny portion, much less than 0.1%, of your DNA, then compare that to a database of DNA that each company creates from all of these tests.

They don’t compare whole genes, which contain up to 27,000 nucleotide base pairs. Actually, these DNA testing companies look at SNPs, which is one single base pair in the gene. Though the SNP may indicate a key difference between genes, it’s sampling one tiny portion of a gene.

Currently, a company such as 23andMe has identified 600,000 SNPs, or about 6% of the 10 million SNPs in the human genome. In other words, these companies are making conclusions without a full analysis of the other 9.4 million SNPs which obviously have much more data that could be critical in disease diagnosis and ethnicity.

This is the first step where error is introduced into the equation. If these DNA kits say you are 38% German, what’s the error around that number. Does it vary from 0% to 76%?

Just to be clear, paternity tests are extremely accurate. They compare a handful of DNA loci between two individuals. The more that the loci are exactly alike, the higher degree of relationship between the two individuals.

But let’s assume that the results are accurate. What can these home DNA kits really tell you about your ethnicity?

Are you related to William Shakespeare?

The answer is that a DNA test isn’t ever going to answer this question. If you can prove you’re a direct descendant of Shakespeare, it’s not going to be through home DNA testing.

Let’s look at this way. Shakespeare’s children are, based on random genetic inheritance, only 50% related to Shakespeare (the other 50% related to the mother). Shakespeare’s grandchildren will only be 25% related to him.

If you consider that there’s been 16 generations since Shakespeare (assuming 25 years to a generation), any direct descendants of him would share 0.00153% of his unique genes (see Note 1). In other words, DNA testing could not possibly tell you if William Shakespeare is your great great great etc. grandfather.

The only way to make that claim is through actual historical records and genealogy. You’d have to establish that relationship between you and him apart from DNA testing.

Are you 38% German?

This is where things are problematic. Do you think that in some way we have markers for Germans that allow us to tell that you’re not French? No, there really isn’t.

Generally these genetic test are better at telling the geographic location of your ancestor’s DNA rather than their ethnicity. Europe today is clearly divided into countries. You know you’re in Germany or France because German or French is the language. There is a non-continuous variation between what constitutes a German or French based on an artificial border between those countries.

But in fact there is a continuous variation genetically between a French village to a German village on the other side of the border. There isn’t a sudden genetic change at the border, but a blend from one location to the next.

There’s a small French city in the eastern part of the country, Mulhouse, which has switched between Germany and France several times over the past centuries. It is now a solidly French city.

Do you think that Mulhouse residents are 100% French or German? No, they are some admixture from the centuries of invasions and conquests.

Now, these home DNA kits may identify you as “French” because it indicates you’re from a region of France. But don’t start speaking  French, because you could be ethnically German.

And, that’s just one example.

Database issues

But the problem gets worse than this. Each company maintains it’s own database, without a determination if they mean anything at all. Do they have a statistically significant number of individuals from Mulhouse, France to pinpoint the SNPs that would indicate if a person was actually from Mulhouse? I don’t think anyone has done that kind of work.

Scientists have identified DNA from a group of early humans called Denisovans. They studied the DNA from one fragment of femur bone inside and out. Does that mean you could get one of these home DNA kits and find out you’re related to Denisovans? No, because we have one sample, and we have no indication what that means to other human populations.

Furthermore, the databases used by the home DNA kit companies have been collected from a variety of sources for a bunch of different purposes. One would be hard pressed to scientifically connect a DNA sample to an ethnic group or location.

Reliability of results from DNA kits

DNA test reliability is one of the larger issues with these home DNA kits. A TV investigative reporter (not exactly high on the hierarchy of scientific evidence) examined results from some DNA testing services. They submitted samples to three different companies from 3 sets of identical triplets.

Theoretically, identical triplets should give you the exact same DNA results, because there is no genetic variation between the triplets.

Each group of triplets showed a surprisingly significant variation in their ethnic make up. Obviously, this should not happen.

One group of triplets had one with a  11% French and German. But the second one was at 18%, while the third one was at 22.3%. That’s a lot of variation.

The second set of triplets had one with 59% British Isles ancestry. The second one was at 66%, and the third one was at 70%. Again, that’s a substantial amount of variability for three women who are genetically identical.

To be fair, the third set of triplets had virtually identical ancestry. The results came from a third genetic testing company.

This was not a scientific study, so take it with a grain of salt or two. But, it does provide us with some evidence about the quality of the results.

Why was there such variability? There are lots of reasons why this may happen. First, cross contamination of the sample. This is a concern that I have had with this type of testing.

Second, the variability of the SNP technology is high enough to cause a variability in results.

What really matters

I remain concerned about this kind of data. It’s possible that finding out that you’re 37.1% Jewish or Chinese is fun for conversation purposes. Even at that point, the data can be used to show some sort of advantage over one another.

But there’s something more troubling about this type of data.

In a new book, Is Science Racist?, University of North Carolina, Charlotte anthropologist Jonathan Marks deconstructs the whole DNA testing industry. He wrote separately,

To understand the ancestry tests, you have to begin by looking at the fine print. This [type of test] says ‘for recreational purposes only’ or something very similar. It obviously is written by lawyers, not scientists, and it’s a way of saying that the results have no scientific or legal standing. This is privatized, corporate science, not ordinary science.

How do they come up with numbers? They take DNA from people from disparate regions and compare yours to theirs. The numbers reflect a measure of your DNA similarity to those of the divergent gene pools. How do they calculate it? Don’t know; the algorithms are protected intellectual property. Are they accurate? About as accurate as looking in the mirror.

So what you have here is generally inaccurate results. Tell you possibly nothing about your ethnic background. And many people use it to determine who or what they are.

We forget the simple fact – we share 99.9% of our genes with all other humans. Races and ethnicities are a social construct, going back thousands of years, that have no meaning scientifically.

Humans aren’t that different, but attempting to make us different based on genetics? That’s just wrong.


  1. Any two humans on this planet share about 99.9% of their genes. All variability comes from the 0.1% difference. So, William Shakespeare’s descendants share 0.00153% of that 0.1% difference. No known DNA test thats could find such a small difference.


Michael Simpson
Liked it? Take a second to support Michael Simpson on Patreon!
Become a patron at Patreon!

Discover more from Skeptical Raptor

Subscribe to get the latest posts sent to your email.

Discover more from Skeptical Raptor

Subscribe now to keep reading and get access to the full archive.

Continue reading