But as these registries of genetic identity grow, it’s becoming harder for individuals to retain any anonymity. Already, 60 percent of Americans of Northern European descent — the primary group using these sites — can be identified through such databases whether or not they’ve joined one themselves, according to a study published today in the journal Science.

Within two or three years, 90 percent of Americans of European descent will be identifiable from their DNA, researchers found. The science-fiction future, in which everyone is known whether or not they want to be, is nigh.

“It’s not the distant future, it’s the near future,” said Yaniv Erlich, the lead author of the study. Dr. Erlich, formerly a genetic-privacy researcher at Columbia University, is the chief science officer of MyHeritage, a genetic ancestry website.