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The science of siblings and their unusual shared quirks

MARY LOUISE KELLY, HOST:

It is not a huge surprise when siblings are alike. Think music prodigies, chess whizzes, star athletes. Some traits that siblings share, though, are so unusual they reveal something about what makes us who we are as human beings. Here's science reporter Ari Daniel with the latest installment in our series on siblings.

ARI DANIEL, BYLINE: It was New Year's Day, and Emma Trenchard was on holiday in Cape Town, South Africa. She was visiting her older brother and his family. They were out to lunch at a cafe.

EMMA TRENCHARD: We were just waiting for our food, and we'd given my niece a coloring book to keep her quiet, which didn't really work that well.

DANIEL: As in, the little 2-year-old proceeded to throw her crayons under the table. So Trenchard slipped off her shoes and started picking them up with her feet.

E TRENCHARD: I mean, if you've got bare feet, it makes more sense to pick it up with your foot than it does to sort of crawl under the table and pick it up with your hands.

DANIEL: Trenchard's always had unusually dexterous feet. As an artist, she's even used them for drawing portraits.

E TRENCHARD: I broke my thumb, and I just got really - I just drew with my feet all the time.

DANIEL: So at the cafe in Cape Town, Trenchard was quite comfortable grabbing the crayons with her feet. And then she noticed - her older brother, Tommy? He was doing the exact same thing.

E TRENCHARD: I was quite surprised 'cause he told me, he said, look, I'll show you how it's done. So it became a sort of toe battle until we realized we both had our bare, knobbly feet out, putting things on the table, and everyone was trying to eat their lunch.

TOMMY TRENCHARD: Judging from people's reactions, this was not normal behavior.

DANIEL: This is Tommy, Emma's big brother.

T TRENCHARD: I suppose I haven't really found many things I can't pick up with my toes.

DANIEL: And I should mention that neither their mom nor dad can do this fancy footwork. It's just Emma and Tommy, which makes it all the more special and revealing. Nancy L. Segal is a psychologist at California State University, Fullerton. She spent her career studying not just siblings but twins in particular. She's trying to understand the origins of certain behaviors and physical traits because she wants to know how we become who we are as individuals. When I told her about Emma and Tommy and what they can do with their feet, she was impressed.

NANCY SEGAL: I find that rather extraordinary because I don't think that picking up things with your feet with that kind of dexterity is that common.

DANIEL: Segal says it's likely that both Emma and Tommy just happened to inherit a similar set of genes that gave them that ability. Sharing such a quirky trait isn't that common for most siblings, but there's one category who shares oodles of these oddities - identical twins. Segal's focused her research on pairs who were raised apart and then later reunited, and she's found that identical twins raised separately have more of these shared quirks than fraternal twins raised together.

SEGAL: We had twins who read books from back to front. A pair of Scottish ladies - and they would eat toast. They'd cut it into four pieces and always leave the last one. That's just how they did things.

DANIEL: Segal connected me with a pair of identical twins who just turned 72. Sharon Poset and Debbie Mehlman were separated at birth when they were adopted by different families. Growing up, Poset says she always felt like something was missing.

SHARON POSET: Yeah, I was always lonely. Always.

DANIEL: And for years, Mehlman felt the same way. She wanted someone her age to go on vacation with, have sleepovers with.

DEBBIE MEHLMAN: I always wished there was somebody out there.

DANIEL: Then, when she was 45, Mehlman found out from her adopted mother that there had been two babies. She hired a private investigator, and before she knew it, she was speaking with her twin sister on the phone. The two agreed to meet, so Poset flew up to Connecticut, where Mehlman was waiting for her at the airport. Here's Poset.

POSET: It was just the most amazing connection.

DANIEL: On the one hand, they were strangers, but they were clearly cut from the same cloth.

POSET: We had decided we had the same lipstick on. We always run late. We listen to classical music. We drink tea about five times a day, hot tea.

MEHLMAN: We both noticed that we're, like, rolling our eyes, and we're - it's like this kind of a thing.

DANIEL: Mehlman demonstrates. She crosses her eyes and then rolls them.

MEHLMAN: We'd both done that since, like, we were little. Like, if something is really stupid, you're like, oh, my God, I can't believe it.

DANIEL: But there were these other, deeper currents of similarity. They were both social workers. They're both religious. Poset's Christian. Mehlman's Jewish. And both say they find a profound comfort in the things they share, and that overlap doesn't make them feel any less unique.

POSET: It's more of a compliment that somebody else does it, too, that you admire and love.

DANIEL: Poset and Mehlman are like dozens of pairs of identical twins who psychologist Nancy L. Segal has studied over the years. Her research, she says, leads to a clear message.

SEGAL: Many of our behaviors that we think we just acquired by random chance are not a matter of random chance.

DANIEL: Segal says the environment plays a role, but she thinks it's our genes that are often behind what makes each of us an individual, quirks and all. Identical twins are more likely than other pairs of siblings to share genes and therefore traits. But every now and again, you do get a pair of siblings who aren't identical twins but do inherit the same random combo of genes, and out pops the same shared quirk.

E TRENCHARD: It's nice to know that you share so much.

DANIEL: Like Emma and Tommy Trenchard, who can pick most everything up with their toes, including crayons during those under-the-table competitions.

E TRENCHARD: And just to clarify, I definitely did win the battle.

DANIEL: So even amongst these shared sibling idiosyncrasies, it can still be survival of the fittest.

For NPR News, I'm Ari Daniel. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Ari Daniel
Ari Daniel is a reporter for NPR's Science desk where he covers global health and development.