Our dissolving genetic privacy

In theory, taking a DNA test to reveal your ancestry is optional. But it’s on the way to becoming obligatory.

Sen. Elizabeth Warren (D-Mass.) announced Monday that she had submitted her DNA to ascertain that she does in fact have Native American ancestry after President Donald Trump had taunted her by saying he would throw a testing kit at her. For those of us not in national politics, a study recently published in the journal Science claimed that within a few years it will be possible to identify some 90 percent of white Americans by using genetic databases that include their cousins. Even if you don’t take the test yourself, someone has taken it for you.

The takeaway from these developments is simple: Genetic privacy is well on its way to becoming obsolete, thanks to the voluntary use of cheap DNA testing technology and the astonishing power of statistics. These factors are changing our social norms and expectations. The only thing that could potentially preserve genetic privacy now would be strict government regulation. That’s pretty unlikely, and even if it does come, it might not be enough to change cultural trends.

Given the unusual circumstances of Warren’s situation—she had been criticized for describing, without genealogical proof, a family tree that includes Native American roots—a DNA test no doubt had some appeal to set the record straight.

But in practice, Warren didn’t go public with her test results until after she had been challenged by Trump. What that means is that the widespread availability of genetic testing gave her almost no choice. Trump was saying something like: If you don’t take the test, it proves you don’t really have Native American ancestors.

There was good reason for Warren to be wary. The test could have come up negative. A negative might have been false. DNA testing designed to reveal ethnic and geographic origins is only as good as the comparison data available to the testers. And there isn’t very much Native American DNA to compare in commercial and public databases, both because there aren’t so many Native Americans and because many Native Americans have chosen not to participate in the databases. Had Warren taken a commercially available test, it might have missed her Native American heritage. That was one motive for her to submit her DNA privately to an internationally respected expert.

If Warren was pushed to reveal her genetic ancestry by the fact of the test’s availability, for the rest of us, our relatives’ actions function as the mechanism for disclosure.

The authors of the Science study drew on existing data for 1.28 million white Americans and were able to find a third-cousin match for 60 percent of white Americans. They project that, once the data for 3 million people are available, it will be possible to find a third cousin for 99 percent of the relevant population and a second cousin for 65 percent.

Notice—and this is the key point— that 3 million people isn’t really a lot of people. It’s just 2 percent of Americans of European descent. But the statistical power of the data is such that it can be used to narrow down identifications to the cousin level. From that point onward, it will usually be possible to use ordinary genealogical records to find an individual.

To the extent the statistical methods are used to find criminal suspects, you might think this is no big deal, or even desirable. But as the study’s authors point out, the same tools can also be used to identify anyone who has, for example, participated in a clinical study in which genetic data is supposedly anonymized.

So if your instinct is not to take a DNA test, that’s understandable. But it’s increasingly also irrelevant. Your third cousins have already taken the test for you. Your genetic privacy isn’t long for this world.

Strict federal regulation could conceivably help. The government could outlaw the kind of searches that are already happening. Realistically, that’s not going to happen, given how useful DNA searches are in solving crimes. Requiring a warrant won’t easily work as a legal reform, because the whole point of a population-wide search is that we don’t know who we are looking for, and because the data is publicly available.

Even assuming we get stricter genetic privacy laws, it may be too late to redirect the trend in cultural norms. Once your genetic data is known, you don’t wake up the next morning in a cold sweat, at least not now. To the contrary, most people who have taken voluntary DNA tests seem to be intrigued and excited by the results. They are often eager to discuss them.

Not everyone holds a news conference or makes a video like Sen. Warren. But then again, she’s contemplating a presidential run.

How soon before we stop demanding all candidates’ tax returns and start demanding their genetic data?

Noah Feldman is a professor of law at Harvard University and was a clerk to U.S. Supreme Court Justice David Souter.