Actress Mia Farrow made gossip-news headlines this week when, asked by Vanity Fair whether her former husband Frank Sinatra was the father of her son Ronan, rather than Woody Allen as broadly understood, she replied, “possibly.” She said that no paternity test had been done.

My first thought when I saw this was, some tabloid reporter without any ethics is going to try to surreptitiously get a sample of Ronan Farrow’s DNA, and of Woody Allen’s, and have both tested. If it were possible to get a copy of Sinatra’s DNA, they'd probably try that too. I guess the only disadvantage for a newspaper might be the uproar that ensues once the story is published—though, that might just make the reporter famous and sell lots of copies.

I’ve long feared that sooner or later we’d start to see the unauthorized collection and testing of DNA—and that it would start with celebrities. Or I should say, I’ve feared that unauthorized collection would expand beyond the police, who already engage in this practice and claim the ability to do so without a warrant. (For more on surreptitious DNA gathering, see this chapter in the book Genetic Justice by Sheldon Krimsky and my former ACLU colleague Tania Simoncelli, as well as this law review article by Albert Scherr.)

DNA is very easy to acquire. We constantly slough off hair (40-100 strands per day), skin cells (30,000-40,000 per minute) and other samples of our DNA. Household dust is made up primarily of dead human skin cells. Our DNA can also be extracted from such sources as coffee cups, cigarette butts, and the flaps of envelopes that have been licked.

That means no matter how hard we strive to keep our genetic code private, we’re always vulnerable to other parties’ secretly testing samples of our DNA. And the cheaper it gets to actually test DNA samples, the more tempting it will be for various parties to do so. By the time we all have access to portable DNA readers that can provide instant readings, we may find ourselves in a situation in which almost anyone can read anyone else’s genetic profile—including information about ethnic ancestry, mutations, disease proclivities, and whatever else we may learn about the human genome. We could see scenarios such as:

Everyone from schoolchildren to dating couples to nosy neighbors routinely checking out each other’s profiles.

Celebrities’ genetic profiles being posted on the Internet

Potential employers running DNA profiles on job candidates (though this would be illegal under the Genetic Information Nondiscrimination Act of 2008 or GINA, as would the use of genetic information in health insurance decisions).

Individuals or companies using collection devices in crowded places to suck up as many human cells as possible, perhaps because they are searching for a relative’s killer, a compatible donor for a sick relative, for blood relatives lost through adoption, or maybe even as marketing leads (in combination with partial, identificatory DNA databases).

Already, as Scherr points out, there have been cases where amateur genealogists and a private investigator working a celebrity divorce have used surreptitious DNA to try to establish paternity.

As it now stands there is no clear law against the surreptitious reading of DNA. When it comes to the police, the Supreme Court recently weighed in on DNA, finding that the Constitution does not bar the taking of DNA from suspects who have been arrested but not convicted of any crime. And as Scherr summarizes the current jurisprudence on surreptitious gathering,

Surreptitious DNA harvesting by the police is currently unregulated by the Fourth Amendment. The few courts that have addressed the issue consistently find that the police are free to harvest DNA abandoned by a putative suspect in a public place. Little in the nascent surreptitious–harvesting case law suggests that surreptitious data banking would be regulated under current judicial conceptions of the Fourth Amendment.

We think that is wrong (as does Scherr), but that’s the jurisprudence so far. When it comes to surreptitious collection by private parties, in the absence of any privacy law in this area there’s even less that our fictional tabloid reporter would have to worry about.