How to find someone who looks just like you

Niamh and her twin stranger Karen. Photo / Twin Strangers

At the time that we are publishing this story, there are 7,238,369,612 people on the planet, according the the US Census Bureau. Chances are, some of them look like you. Not your family members, but total strangers, with your nose shape, your hair thickness, your eyebrow arch.

You rarely come face-to-face with these people, but every so often, you hear about them.

"You look just like my friend!"

"Oh sorry, I thought you were someone else."

"You guys could be twins!"

You are not the victim of a separated-at-birth Parent Trap reenactment. You might just have a doppelganger.

A doppelganger (German for "double walker") is a person who looks incredibly similar to you. We'll say incredibly similar instead of "identical," given that even genetic identical twins aren't actually perfect doubles. We're all unique as snowflakes, right? (Kind of; we'll explain in a bit.)

Well, now, all those unique snowflakes have social media profiles.

If you wanted to find your doppelganger before the internet, you could end up wandering the streets for years awkwardly peering at strangers. Now, the web is stocked with images of billions of people, many offering multiple angles of their face for better comparison.

When two TV producers and an engineering student set out on this very mission, they didn't even need to leave their apartments in Ireland.

Niamh Gearney, Terence Manzanga and Harry English started the "Twin Strangers" project, a challenge to find their near-identical counterparts in 28 days. They made a website and accounts on Facebook, Twitter, Instagram and YouTube, all with the same request: Do you know someone who looks like one of us?

"On the first day, I spent from 10am to 2am just asking my friends to share this, knowing at least a third of their friends would see it," said Gearney, calling from Dublin. "The power of social media is so crazy, so intense, you would not believe it."

Two weeks later, they were bombarded with more than 6,000 messages a day.

Photos poured in, not just of their "twins," but of people of all shapes, colors and sizes who wanted to find their own doubles. Gearney filled Facebook albums of their selfies and fuzzy thumbnails, hoping to connect other doppelgangers while she searched for her own. The fascination, she said, is based in a desire to find out what the other you is really like.

"It's a popular belief that all of us have seven people in the world who look like us," she said. "Wouldn't it be amazing to find them? To know what they are doing with themselves?"

For her, the answer was living only an hour away. A Facebook friend linked Gearney to Karen Branigan, a 29-year-old with her same eye color, nose shape, and according to Gearney, same facial expressions.

When they met in person to pose for photos that would soon circle the internet, they couldn't stop staring at each other.

"She can crack her entire back and I can do the same," Gearney said. "We both loved drawing growing up, and what did we both draw all the time? Fairies. We both used to draw fairies. That's insane."

You don't have to be much of a skeptic to arch an eyebrow at their magical similarities. They both loved fairies, but so do millions of other little girls. They make an impressive picture while wearing matching shirts, but if they stand up, they are completely different heights.

So other than finding each other through the power of social media, what's the big deal about doppelgangers? If we can pair them up more easily, we can figure out how they look so similar without being family members. This is good for our curiosity, and even better for science.

The way we look, especially in our faces, is determined mostly by genetics and environment.

Environment is one of the common-sense factors we tend to forget, said Daniele Podini, a forensic molecular biologist at George Washington University.

"You can take two identical twins and raise one near the equator and one in Greenland," Podini explains. "They will have different diets, physical activity, sun exposure and temperature at which they live, and so on, and that is going to affect their development."

That helps account for Gearney's similarity to her twin stranger, who was also raised in Ireland.

But we also know that, even without being family members, they likely have some matching DNA.

"It's just a question of statistics," Podini said. "You have a limited amount of traits in the face. Shape of nose, height of cheeks, color of eyes. So with a billion people in your same ethnic group, there's a chance that somebody shares similarities in all of these traits."

And each of those traits comes from their genetic makeup.

Research has yet to identify exactly which genes influence exactly which physical traits, but they're on their way to figuring it out. An ongoing study based at Pennsylvania State University has a database of more than 6,000 3D images of faces. For each face, they have the person's genetic makeup.

"There aren't an unlimited number of faces," said Mark Shriver, the project's lead researcher. "In a set of 600 people, we only needed 44 separate variables to express all the variation that could exist in the face."

In other words, it's completely possible that someone else is walking around wearing your face.

Podini and Shriver say they are already able to use a DNA sample to estimate a person's geographical heritage and eye color. As this type of forensic research continues, likely with the aid of genetic twins and doppelgangers, we may see a day where a hair left at a crime scene could generate a detailed portrait of a suspect for police to track down.

Until then, Gearney's two friends will be the ones on a search. They have until April 27 to find doppelgangers as closely matching as Gearney and Branigan.