If you were on the Internet this week, you probably saw this video of Steve Harrington "meeting" his son Jean-Ralphio Saperstein:

The discussion began in online forums, sparked by the uncanny resemblance between the actors who play Steve and Jean-Ralphio, Joe Keery of "Stranger Things" and Ben Schwartz of "Parks and Recreation," respectively.

This is just one recent public example of doppelgangers, or a look-alike of a living person.

ATTN: spoke with Michael Sheehan, an assistant professor of neurobiology and behavior at Cornell University who has studied human facial diversity and clarified how it's even possible to be twinning in real life.

"The statistical explanation is that if you shuffle a deck of cards enough times, you're going to deal the same hand twice at some point," Sheehan said. "There's a lot of diversity in the forms of human faces, but there's still a limit to it."

For the most part, however, humans are an especially diverse species when it comes to our faces, according to Sheehan.

In fact, he has conducted research exploring why there aren't more doppelgangers in the world. One explanation, he has found, comes down to the high cost of being too similar to other people.

"If people are hard to tell apart, there's more chaos and confusion," he said. "There's the opportunity cost, meaning an opportunity meant for you goes to someone else, or the cost of punishment, when a negative consequence intended for someone else gets directed to you."

But another possible explanation of doppelgangers is based in perception.

"It's not only facial appearance, but also styling, how people are presenting themselves or acting," said Sheehan. "Context has a lot to do with looking alike as well."

As an example of how huge a factor presentation plays, he brings up the popular sci-fi show "Orphan Black," in which actor Tatiana Maslany convincingly plays several clone characters who have distinct personalities and looks. Sheehan explains that "even though she's playing all these characters, she doesn't look like herself at all because of her different mannerisms, the way she speaks, and how she carries herself." By that same logic, someone who has the same hairstyle, clothing, and gestures as another person could appear to look the same, even if their faces aren't exactly the same.

The next phase of doppelganger research will likely involve delving into the perceptual side of doppelgangers and how changing social dynamics such as coming into contact with more people (and faces) come into play. "We have much larger exposure to people than even 10 years ago, so it's plausible that we’re less familiar with the faces we see and end up lumping them together," Sheehan says.