At the heart of this cozy coffee shop lies a big sister's love for her little brother

The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We'll be sharing these stories over the next several weeks.

There's a coffee shop in the historic center of Charles Town, W.Va., where Libby Powell's family memorabilia hang from the exposed brick walls.

On one shelf, there's a photo of Libby posing with her towheaded baby brother. A jar of oatmeal-and-butterscotch cookies called Salty Siblings perches by the cash register. An elegant copper roaster parked in the shop's front bay window churns out the store's custom blends, including a popular one with Ethiopian beans named after that baby brother: The Benjamin.

Powell named this place Sibling Coffee Roasters — and it stands as a testament to one of her most cherished relationships.

Powell was already 14 and in high school when her brother, Benjamin Withem, was born 34 years ago. By that time she'd already thought a lot about the significance of having a sibling in her life. She knew, through intuition and experience, what the scientific research now shows: That this connection can deeply affect our mental and physical health over the course of our lives, for good or for ill.

"We have a human need to bond," she says. "Your friends are going to come and go. But when it's family, if your sibling is your friend, they're going to be there forever."

About 80% of children in the United States grow up with a sibling. It's a relationship that usually comes with shared experiences of family and childhood — and maybe also shared bedrooms and rivalries. Research about siblings' influence on our development and psychology is a relatively new field. But scientific studies show those relationships shape us in myriad ways, seen and unseen. And the impact of those relationships — good or bad — endures well beyond childhood, into middle age and beyond.

In adolescence, siblings are very influential when it comes to risk-taking behaviors that can include things like sex or substance abuse. Even in middle age, being on good terms with our siblings continues to strongly correlate with our mental and physical well-being, especially during life transitions like a divorce or caring for ailing parents. Late in life, siblings can help support one another to maintain their health and companionship, and recounting shared memories can be a powerful antidote to loneliness.

"Siblings matter. They matter above and beyond our parents. They matter above and beyond our peers," says Shawn Whiteman, who studies human development at Utah State University.

A sibling worth waiting for

On this bustling Saturday morning, Powell picks up a bag of The Benjamin off the shelves by the cash register and reads its label: "Sibling's brotherly love blend." It is mild, in keeping with her brother's personality, with a blueberry-like flavor. "I definitely wanted that to encompass what his taste for coffee is," she says.

Powell says she once experimented with a dark roast she called "The Sibling Rivalry," but it didn't fit any part of her ethos.

"I hated it," she says. "And I don't like to fight with my brother, so I decided — we're not going to carry a dark roast."

As a girl, Powell — a Baptist preacher's daughter — yearned to have a brother or sister, and her parents, Mike and Naysa Withem, tried to have more children.

When Libby Powell was about 2, they started taking in foster children. Those experiences were inevitably marked by disappointment, because for one reason or another they could not stay, says Naysa Withem.

The last foster child, an older boy named James, stayed for seven years, and Powell grew up thinking of him as her actual big brother, complete with all the skirmishes and antics that come with traditional siblings.

"I remember the arguments, and getting into trouble with him, and doing things with him that were sneaky," Powell says.

But when he was 16, her foster brother chose to leave the family, a decision that left a 10-year-old Powell devastated: "I was alone. It was like all eyes were back on me, and I didn't know what that felt like because I don't think I remember being an only child." His absence, and the sense of isolation, fed her desire for siblings.

Her parents, meanwhile, were trying to have another child. "I remember my mom had gotten pregnant and I was so excited," Powell recalls. "I remember that feeling and thinking, 'I'm gonna be a big sister.'"

It was not to be: Powell was with her mother when she miscarried. "That was traumatic," says Naysa Withem.

So when Baby Benjamin arrived two years later, his sister was waiting with open arms.

"I just remember just thinking: 'This is the prettiest baby I've ever seen in my life,'" she says, her voice rising with emotion. Her brother shuffles from around the counter in the shop's back kitchen and pulls her in for a tight hug.

Awash with gratitude that he was born alive and healthy, Powell says she doted on her brother like a doll, lathering him with lotions and changing his diapers and clothes.

Around the time Benjamin Withem was potty trained, Powell headed to college. Even though the time they overlapped in the same house was limited, her brother says he had developed a close connection with her that endured: "It's nice to always be reminded that you have these shared experiences that are constantly pulling you back together."

An evolving relationship

The study of sibling relationships and their influence on how we think or act hasn't been as studied as other family relationships — like those between mothers and children, for example. Researching siblings also isn't easy, because no two families are alike. Variations like gender, age gap, or the number of siblings can really matter, making comparisons between families difficult and conclusions harder to draw.

One classic example where that can get complicated is birth order — something popularly believed to have a great deal of influence on our personalities. While some earlier studies suggested it might have some impact, most research doesn't bear out the idea that birth order has any lasting significance on who we become, says Utah State's Whiteman.

Still, siblings are overall very influential because they're usually our first peers. We might idolize them or battle them, but either way, through them we learn how to relate to others.

"Peers, if you have too many conflicts with them, they are just not going to be your friend anymore, but siblings really can't get away from it," says Nicole Campione-Barr, a psychologist who researches family dynamics at the University of Missouri. "So it's really one of our only training grounds socially to understand how to handle conflict in effective ways."

Libby Powell, for example, recalls how her brother used her as a sounding board — especially in his teen years, and especially after he'd made a mistake.

"If he was going to be in trouble or if he made a bad decision, he came to me first — and he was feeling out what my reaction would be," she says.

"I think he was testing the waters," she says, before having to tell their parents.

Naysa Withem, who's been watching her two children reminisce as she cleans the shop's kitchen, chimes in with a correction: "He was hoping you would cushion that with mom and dad," she says with a laugh.

The dynamics between siblings often change in young adulthood, as they explore independent paths. That was true also for Ben Withem who, after college, took a cybersecurity job in the Middle East — a world away from his sister in Charles Town.

"That was definitely the most distance we've experienced," he says. And being that far was "almost like hitting the reset button" on their relationship, he says.

Powell found that "reset" difficult and says she felt angry. "I felt those same feelings when James left — when my foster brother left," she explains. At the same time, her brother had recently married, which meant Powell had to adjust to make room for another important person in his life. "That was hard for me because I'm sharing my little brother, who I thought that I had a little control over."

It was the only time they remember any tension existing between them. They had one fight, which culminated with Powell accepting her brother as an adult peer.

"He was taking a stand as an adult for the first time ... and I was put exactly where I needed to be put," Powell recalls, nodding approvingly toward her brother. Benjamin Withem, the more introverted sibling, agrees silently, deferring to her memory.

Through their adult lives, coffee played a big role in keeping them connected. Withem loved good coffee, and Powell says she relied on bad coffee for decades to get her through working overnight shifts as a nurse. He tried roasting beans in his popcorn popper; she eventually began following her younger brother's lead and upgraded to their current, kitchen-table-size industrial roaster.

Powell discovered she loved the taste of her own freshly roasted beans, as well as the coffee culture and social life that surrounded it.

"I just found that coffee — the way that he would describe it — it wasn't just a drink, but it was a relationship," she says.

When she opened Sibling Coffee Roasters five years ago, Powell saw it as a kind of extension of that relationship, a chance to share the warmth and support she associates with siblinghood. She says the shop connects her to the community she's lived in her whole life, and it gives her an excuse to talk to people about their lives and their troubles.

"I always wanted to feel cared for, and I always have felt that way," she says, "and I know that there's just way too many people out there that don't."

Sibling Coffee Roasters also reflects the dream that Benjamin Withem will eventually open up another shop as they grow old together.

It's a sentiment he shares, he says. "I see the name she picked as the open invitation."

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