Psychology

Identical Twins Can't Tell Themselves Apart, Either

In the most annoying things an identical twin hears on the regular, "Can you tell each other apart?" is right up there with "Can you read each other's minds?" and "Who's the evil one?" But according to several studies, it's not as silly a question as you might think. Identical twins actually do have trouble telling who's who in photographs — and it can be even harder depending on their relationship style.

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Who Am I? Who Are You?

Despite the popularity of the question, there hasn't been a ton of research into what happens when twins see each other's faces. There have, however, been plenty of studies into what happens when a non-twin sees his or her own face in comparison with other faces. Basically, it jumps out at you.

People recognize their own faces in a lineup much faster than even those of celebrities or close friends, a phenomenon scientists call "self-face advantage." That makes sense since you see your own face more than any other. Plus, there's an evolutionary advantage: can you imagine what would happen if you regularly mistook your reflection for a threatening stranger?

But an identical twin has a different situation. He sees his own face more than any other, sure, but his twin's face probably comes at a close second. And studies have shown that while people recognizing other faces usually take in the whole face as a unit, people recognizing their own face use individual features — and identical twins share a whole lot of features. And while babies can generally recognize themselves in the mirror by age two, a 1987 study showed that identical twin babies only differentiated between themselves and their twins after looking at them for a long time. So for an Ig Nobel Prize-winning study published in PLOS One in 2015, Italian researchers set out to determine whether identical twins had that "self-face advantage" when it came to each other's faces.

Faces In A Crowd

The researchers recruited 30 volunteers in total: 10 pairs of identical twins, and 10 non-twins to act as controls, all with an equal number of men and women. The volunteers were shown a series of cropped black-and-white pictures of themselves, their twin, and a close friend or family member (sometimes right side up, sometimes upside down) for one second apiece and asked to identify who they were each time. The controls saw themselves and a pair of twins. They did this in four sessions, seeing 336 pictures in all.

Interestingly, twins took longer to recognize themselves than they did to recognize their friends, even though non-twin volunteers did the opposite. It also took the twins just as long to recognize their own twin as it did for them to recognize themselves. That suggests that twins don't have a "self-face advantage" — the time it takes them to distinguish whether they're seeing themselves and their twin destroys any advantage there might have been.

The volunteers also took personality tests, so the researchers were able to delve even deeper into the data. They found that if a twin scored high on markers of avoidant or anxious relationship styles (that is, if they were either overly dependent on relationships or had an unusually low attachment to them) they had a harder time identifying their own face. But that suggests that the opposite is also true. Well-adjusted twins, take heart!

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We Already Have Human Clones: Identical Twins

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