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Most White Americans’ DNA Can Be Identified Through Genealogy Databases

To determine the odds of correctly identifying an individual from a given DNA sample, Dr. Erlich and his colleagues — from Columbia University, the Hebrew University of Jerusalem and the New York Genome Center — analyzed 30 DNA kits chosen at random from the GEDmatch database.

Their results were eye-opening. The team found that a DNA sample from an American of Northern European heritage could be tracked successfully to a third-cousin distance of its owner in 60 percent of cases. A comparable analysis on the MyHeritage site had similar results. (The analysis focused on Americans of North European background because 75 percent of the users on GEDmatch and other genealogy sites belong to that demographic.)

Some experts have raised questions about the study’s methodology. Its sample size was small, and it didn’t factor in that more than one match is often required to identify a suspect.

CeCe Moore, a genetic genealogist with Parabon, a forensic consulting firm, also expressed worry in an email that the Science paper may obscure the difficulty involved in puzzling out someone’s identity; it takes a highly skilled expert to build a family tree from the initial genetic clues.

Still, she said, the takeaway of the study “is not news to us.” In recent months Ms. Moore has been involved in a dozen murder and sexual assault cases that used GEDmatch to identify suspects. Of the 100 crime-scene profiles that her firm had uploaded to GEDmatch by May, half were obviously solvable, she said, and 20 were “promising.”

“I think it’s a strong and convincing paper,” said Graham Coop, a population genetics researcher at the University of California, Davis. In a blog post in May, Dr. Coop calculated just how lucky investigators had been in the Golden State killer case. He reached a statistical conclusion similar to Dr. Erlich’s: society is not far from being able to identify 90 percent of people through the DNA of their cousins in genealogical databases.

“This is this moment of, wow, oh, this opens up a lot of possibilities, some of which are good and some are more questionable,” he said.