Doppelgängers share strikingly similar physical characteristics—they look so alike that, at times, these two unrelated people could easily pass for twins (or, at least, siblings).
Now, new research suggests that doppelgängers have more in common than meets the eye. People with very similar faces also share many of the same genes and lifestyle traits, according to a new paper published Tuesday in the journal Cell Reports.
It may seem obvious that people with similar facial features would also have some of the same DNA, but no one had scientifically proven this, until now. Thanks to the internet, it’s now easier than ever for researchers to track down and study doppelgängers.
To understand what was going on at the genetic level among look-alikes, scientists collaborated with the Canadian photographer François Brunelle. Since 1999, Brunelle has been traveling around the world to capture intimate portraits of strangers who look nearly identical to one another for his “I’m not a look-alike!” project.
Researchers asked 32 pairs of Brunelle’s models to answer questions about their lifestyles and submit samples of their DNA.
Using facial recognition software, the scientists analyzed headshots of the so-called “human doubles” and computed a score to quantify similarities among their faces. They compared the scores to those of identical twins and found that the software had awarded twin-like scores to exactly half of the doppelgänger pairs.
To find out whether the similarities ran more than skin deep, the researchers next studied the participants’ DNA. They found that nine of the 16 very similar-looking pairs shared many common genetic variations known as single nucleotide polymorphisms. These pairs are “therefore like virtual twins,” says Manel Esteller, a geneticist who leads Spain’s Josep Carreras Leukaemia Research Institute, to Gizmodo’s Ed Cara.
In terms of their lifestyles, the "human doubles" were also more likely than non-doppelgängers to have characteristics in common, such as their weight, height, smoking history and education levels.
But though they had similar genetics and traits, the look-alikes had very different microbiomes, or communities of helpful and harmful microbes that live on and in the human body, and different epigenomes, or variations in expressed traits influenced by the experiences of past generations. From a nature vs. nurture perspective, this suggests that it’s DNA, not environmental factors or shared life experiences, that is primarily responsible for how similar doppelgängers look.
In a growing population, there’s bound to be some genetic overlap just by happenstance. “Because the human population is now 7.9 billion, these look-alike repetitions are increasingly likely to occur,” Esteller says in a statement.
Aside from pulling back the curtain on one of life’s great curiosities, the research could have important medical implications in the future. People with similar DNA may be equally susceptible to certain genetic illnesses, so doctors could use facial analysis as a quick and easy pre-screening tool, reports the Telegraph’s Sarah Knapton.
Researchers say the findings may also someday help police investigators conjure up the faces of suspects from their DNA samples. But that potential application wades into murky ethical territory, says Daphne Martschenko, a biomedical ethicist at Stanford University who was not involved in the study, to the New York Times’ Kate Golembiewski.
“We’ve already seen plenty of examples of how existing facial algorithms have been used to reinforce existing racial bias in things like housing and job hiring and criminal profiling,” Martschenko says to the Times.