In spring this year, police managed to track down the suspected Golden State Killer – a fugitive responsible for 12 murders, 51 rapes, and over 120 burglaries – thanks to publicly shared genetic information gathered from spit-in-a-cup consumer DNA testing kits like 23andMe and Ancestry. Although he had never used one of these kits himself, some of his distant relatives had, allowing detectives to compare their DNA to DNA gathered from the crime scenes and identify the killer.
It turns out, this was not just a lucky break. A new study, published in the journal Science, has found that an estimated 60 percent of the US population with European heritage could be identified in a similar way using their relatives' data from consumer DNA testing websites, even if they've never joined a genetic database themselves.
This is all done through a technique called long-range familial search, which allows researchers to match an anonymous individual’s DNA to distant relatives. That link could then be used as a major clue to piece together the identity of the anonymous individual. Since April 2018, this method has been used to solve at least 13 criminal cases, most notably the so-called Golden State Killer, who had remained unidentified and uncaptured for 44 years.
Over 15 million people in the US have used a consumer genetic kit and, in turn, submitted their genetic information to a genomics database. As increasingly more people jump on the trend, it makes it possible to identify more and more people just using their distant relatives' DNA. In fact, it will be possible to identify the third cousin of most people if just 2 percent of the population submit their DNA to a genetic data.
“We are getting very soon to the point that everyone will be potentially identifiable using this technique,’’ study author Yaniv Erlich, an assistant professor at Columbia University and the chief science officer at the consumer-DNA-testing firm MyHeritage, told Bloomberg.
To reach these findings, the team sifted through a dataset of 1.28 million anonymous US citizens from MyHeritage's database, which overwhelmingly contained people of northern European descent. They then looked for relatives more distant than first cousins elsewhere in the database. For 60 percent of the people studied, a search was able to find a third cousin (people who share a great-great-grandparent) or closer. For perspective, you would have around 190 third cousins if you use a simple model where a family has 2 or 3 children.
"Because the average person has so many of these distant cousins, it becomes reasonably probable that one or more of them is in a publicly searchable database, even if only a small fraction of the US population is included," Graham Coop and Michael Edge, DNA experts at the University of California, Davis, who did not work on the study, wrote in a statement to The Associated Press.
As the case of the accused Golden State Killer brilliantly highlights, long-range familial searches are an incredible tool for law enforcement. However, all of this raises some concerns about privacy. You never know, someone might be able to track you down just because you fourth cousin whom you've never heard of took a consumer DNA test.