I went to the world’s largest gathering of identical twins. I left jealous.

When Mylee and Cayla Simmermon were toddlers, even they couldn’t tell themselves apart. Their mom would catch Cayla staring into the mirror, waving, and shouting, “Hi, Mylee!”

She was mistaking her own reflection for her sister.

I met Mylee and Cayla on Aug. 6 at the annual Twins Days festival in Twinsburg, Ohio. It’s the world’s largest gathering of twins — thousands of identical pairs (as well as fraternal twins and other multiples) gather to celebrate this special kind of siblinghood.

Identical twins share a particularly intense bond. They are the result of one fertilized egg splitting into two, giving them identical DNA. (Fraternal twins are the result of two separate, genetically different fertilized eggs.)

As a result, identical twins are as close as two people can be. They can speak in unison (it’s weird at first, then charming). They often choose the same careers — the Simmermon sisters, now 25, are electrical engineers in Knightstown, Indiana.

They and other identical twins I met at Twins Days are really, really into their twinness. Maybe it was because I was there as an outsider singleton — that’s twin speak for “non-twin” — but I was kind of jealous of their love.

During the festival, I asked 15 or so identical twin pairs the same question: What’s the best part about being a twin? The overwhelming answer, often said in unison: “It’s like having a built-in best friend for life.”

That sounds awesome. Who wouldn’t want that?

And I couldn’t help but wonder: In the not-too-distant future, where sex may no longer needed for human reproduction and embryos are selected based on genetic traits, would it be better for everyone to have a twin? Would the world be a better place? Twins Days provides compelling evidence that the answer is yes.

Twins Days is a celebration of twins — and their sameness

Joss Fong / Vox

Twins and other multiples, like triplets and quadruplets, have an uncanny, absurd closeness. That’s what Twins Days, now in its 41st year, is all about. Many twins, like the Simmermon sisters, have been returning every year to celebrate their twinness.

”We’ve been coming since we were 3, and once you come, you’re hooked,” Cayla Simmermon said.

The festival grounds sprawl out behind the local middle school. It’s a perfect portrait of Midwest Americana — squared.

A perfume of funnel cake grease spreads over the hot, breezy air. Teenage twins roam in cliquish coed packs. A pair of 20-year-old men told me they hoped to come away from the festival with a few phone numbers. Not too far away, a pair of gray-haired women are walking in tandem, with canes in tow.

The vibe is a mix of summer camp, family reunion, small-town carnival, and — because the twins are encouraged to dress in costume (this year’s theme is space) — a comic book convention.

There’s also a serious sideshow: Twins Days is a rare opportunity for researchers to come and study lots of twins, who’ve long been considered to be “natural experiments” for teasing out the influence of genetics and the environment on life outcomes. And so at Twins Days, you’ll also find sociologists, geneticists, forensic investigators, and computer scientists trying to build facial recognition software so sensitive it can tell twins apart.

There’s some evidence identical twins enjoy lifelong benefits from having each other

Brian Resnick / Vox

The scientists who’ve run twin studies over the years have learned a lot from identical twins about what kinds of traits — from taste to personality — are genetic. But, surprisingly, they know much less about the power of the twin bond.

Some clues are starting to emerge. Researchers have found that an extreme level of closeness and understanding — having a “best buddy for life” — may be protective over the life span. Recently researchers at the University of Washington analyzed a data set of 3,000 Danish twin pairs born between 1870 and 1900. This cohort was born a long time ago, but the age of the data set allowed the researchers to find out the death dates of the entire cohort.

”We show that monozygotic [identical] twins have greater cumulative survival proportions at nearly every age compared to dizygotic [fraternal] twins and the Danish general population,” the authors write in the journal PLOS One. They conclude that the social bond of being a twin “is a plausible driver of the survival advantage.”

PLOS ONE

It certainly makes sense. The strength of social relationships has been shown over and over again to be a protective factor for lifetime health and mental well-being, and is thought to also protect against the cognitive declines that come with dementia.

A 2015 meta-review of 70 studies found that loneliness (in anyone) increases the risk of mortality by 26 percent. “Some say loneliness has the same effect on longevity as smoking,” Maike Luhmann, a loneliness researcher, told me in May.

So it’s not a stretch to think being an identical twin may protect people against it.

But before this question — of whether the twin bond is protective — can be explored further, researchers need to gather a better understanding of what specifically, makes the twin relationship unique.

What makes the twin bond special?

Joleen Greenwood, a family sociologist at Kutztown University in Pennsylvania, was at the festival conducting research, and is a twin herself. Growing up, she and her sister Nikki always felt their relationship was more intense — and perhaps more important — than their relationship with their other sibling or even parents.

”Having that built-in best friend, sometimes you feel like you don’t need anybody else,” Greenwood says. Perhaps that’s enough.

(Quadruplets I talked to at the festival confirmed this. The four teenage sisters have only one other friend they share among themselves. “It’s less drama that way,” one of them said.)

Joss Fong / Vox

Greenwood is conducting hundreds of interviews with twins about their experiences and relationships, wondering if there are commonalities. Perhaps being a twin complicates romantic relationships. Perhaps the twin bond matters more at certain times of life than others.

”There hasn’t been a lot of research looking at the social relationship,” she says. By asking question like, “Does being a twin affect the number and quality of your friend relationships?” she hopes to find out.

“Being a twin is our identity”

There are times when being a twin isn’t all that great, many festival-goers told me. The biggest complaint: Twins hate it when others refuse to see them as individuals.

With their matching bright orange tanks, tatted-up arms, and white goatees, Mark and Mike Smith, 61, are impossible to mistake as anything but twins. They had been crowned the kings of the festival (like a homecoming king), and I found them setting up court in one of the coveted shady areas.

They reign over this celebration now, but they admit during their youth that they struggled with finding their own identities. Growing up, “we were called ‘twins’ instead of ‘Mark and Mike,” Mike Smith says, sitting next to his brother. They hated that.

“When we were small we were totally similar, then in our 20s we did everything we could not to be similar, and now we find it’s really cool to have a best friend and be similar in what we do,” Mike says.

They now lead parallel lives. Mike is a minister. Mark works at a hospital. They have their own homes, their own kids. But they still meet up every Thursday to shoot pool.

”Mark’s my best friend, will always be my best friend; we agree to disagree,” Mike says. “It’s gotten better as we’ve gotten older.”

Joss Fong / Vox

Other twins echoed a similar pattern — inevitably, after a period of self-discovery, they always come back to each other.

”We try to do our own things — and we have things that we don’t like about one another, and things that we do that are separate — but for some reason or another, we always come back together,” said James Johnson, 34, a radio producer who was there with his brother Charles.

”Everyone’s all about, ‘You have to be unique, you have to be an individual, twins are too bonded, it’s going to hurt them,’” Kristal Adams, 42, said. “But they don’t understand —being a twin is our identity.”

Greenwood, the sociologist, is also studying to what degree twins become codependent on one another. Particularly, she wonders how detrimental it is for a twin when his or her identical sibling dies. After all, even though twins are born on the same day, it’s unlikely they’d die on the same one too. Losing a twin, she says, is unthinkable in a way that’s more intense than losing a parent.

In the future, we might be able to make more twins

It’s hard to underscore how powerful the shared experience of both having the same DNA and having grown up in the same environment is.

In 2015, Nature Genetics published a meta-analysis of studies conducted on a total of 14 million twins. “Our results provide compelling evidence that all human traits are heritable: not one trait had a weighted heritability estimate of zero,” the paper concluded. It means that all the characteristics that make us who we are are influenced by genes, at least in a tiny way.

Growing up in the same environment ensures even more similarities. Twins can read each other’s minds not because of a magical connection, but because those minds have been exposed to such similar things and are hardwired to react in similar ways.

”It’s like we have constant validation, which a lot of singletons have to struggle with,” said Tia Dmuchowski, a 20-something bassist in a rock band she plays in with her sister, Tanya. “Am I alone, am I the only one who thinks this? But we think almost everything the same.”

Joss Fong / Vox

Serious scientists have been discussing the prospect of how, with the help of genetic technologies, babies could be “made to order” in a few decades. “We humans will begin, very broadly, to select consciously and knowingly the genetic variations and thus at least some of the traits and characteristics of our children,” bioethicist Hank Greely writes in his new book The End of Sex.

Already, babies born through in vitro fertilization are more likely to be identical twins than the population at large. Scientists aren’t quite sure why this is. But if they can figure it out, and then encourage twinning through some means, should parents consider it as an option?

I can imagine the future questions at a fertility clinic: Hair color: brown; eye color: brown; check this box if you want two. Attending Twins Days is like getting a glimpse into this brave new world.

(To be sure, the twins attending this festival are biased: They really enjoy being twins. Other twins who weren’t there may not.)

So should everyone be a twin? Everyone should try it, the Dmuchowskis joke.

At the “double take” parade, where twins march down the main stretch of Twinsburg, I talked to Brian D’ziurman, a father of two 6-year-old twins who were running around wildly, collecting candy thrown from the parade marchers. In the parade, I saw several sets of Stormtroopers, pairs of Elliotts from the movie E.T., a pair of uncanny Thor lookalikes, and a set of Miss Piggys (from space!).

I asked D’ziurman what he thinks his sons like most about being twins. “It’s like having a sleepover with your best buddy every night,” he said.

If you told that to my 6-year-old self, I’d say, “That’s awesome.”

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