Dorianne Kristiansen grew up in a family in Midtjylland, where her parents set the rules.
When her father said no, you didn’t ask again, and if you were told to peel potatoes, clear the table, or move schools because he had found a job elsewhere in Jutland, you did it.
But if she needed something other than a yes or no, like a discussion or some good advice, she turned to her siblings. They were a group of nine, enough to form a complete rounders team. They taught each other how to resolve conflicts and accept the differences in each other’s personalities.
»We raised each other both directly and indirectly all the time. We’ve significantly shaped each other,« says Dorianne Kristiansen, who is now 66 years old and lives in Kolding.
She thinks of her siblings a bit like a carton of eggs. Each has their own spot. And there’s both a struggle to break out of that spot and distinguish oneself from the group, as well as a great comfort in knowing there’s a place next to the others.
»I can tell you, many people didn’t dare to pick on me in the schoolyard because they knew that messing with one of us meant messing with a lot of siblings,« says Dorianne Kristiansen.
From an early age, our siblings have a crucial impact on who we become as individuals. It’s often the longest family relationship in a person’s life, and including step and half-siblings, 93 percent of 16-year-old Danes in 2025 will have one or more siblings, according to Statistics Denmark.
According to a survey conducted by Megafon for Politiken, 21 percent of Danes wish they had more siblings while growing up, and research has shown that children spend about one-third of their free time with their siblings. That’s more time than they spend with parents, friends, and even themselves.
Despite this, sibling relationships have been relatively under-researched until recently, often viewed as a less significant subgroup within the family. Anthropologist Ida Wentzel Jensen, who led the research project ’Moving Siblinghoods’ at Aarhus University and authored the book ’Hvad er søskende?’ (’What Are Siblings?’), explains.
»For many years, family studies focused vertically, top-down, whereas horizontal relationships like those between siblings have received less attention. But siblings shape each other constantly in daily life. They grow up together, argue in the back seat of the car, and often share difficult things,« she says.
In recent years, researchers worldwide have begun to recognize just how important siblings are to our lives.
Some common misconceptions about birth order of siblings have been debunked, while others have been substantiated.
Today, international research clearly shows that the eldest in a sibling group generally fares better economically and educationally than the younger siblings and has a higher IQ by the age of one. Younger siblings, on the other hand, are often better at elite sports. This phenomenon, known as ’niche-picking,’ suggests that second and third siblings often excel in different areas than the academic path typically taken by the eldest sibling.
In general, there’s a heightened focus on the fact that parents and genetics are only part of what determines who we become as individuals. New York Times journalist Susan Dominus has written extensively on this in her widely acclaimed book ’The Family Dynamic: A Journey into the Mystery of Sibling Success.’ She argues that too much importance has been placed on parents in shaping human development, while the influence of siblings has been underestimated.
This aligns with a groundbreaking discovery in sibling research. We’ll return to that.
A relationship in lifelong development
During her childhood, Dorianne Kristiansen’s role in the sibling group evolved.
As the third eldest, she initially was the younger one who received help and protection for several years. But when her two eldest siblings moved from Skive to Viborg to attend high school, she suddenly became the eldest, taking care of, tucking in, and raising her younger siblings.
»We were all about a year and a half apart, so you quickly became the older one,« she explains.
The roles in her sibling group were clearly defined by an age-based hierarchy. Each knew their place in the egg carton and still does to some extent. Dorianne Kristiansen shares how her eldest sister remains the family’s head today, having taken the greatest responsibility and earning particular respect.
Sometimes, one of them would adopt a new role within the group and assume more control for a period.
»I was probably more someone who found their spot as a child and stayed there. In that way, we were shaped early on into the people we are today,« she says.
As adults, Dorianne Kristiansen and her siblings have worked to maintain their close relationship.
»We’ve had plenty of conflicts, but we’ve learned to resolve them, so I don’t have a single brother or sister I’m estranged from. I’ve been at odds with some, but we’ve always resolved it. I never doubt that they are there for me. We have a tremendous loyalty toward each other. They are the richest thing I’ve taken from home,« she says.
One of the things they’ve managed to do as adults is to allow space for their different narratives about their shared childhood.
»We are nine children with nine different upbringings. I view my father very differently than several of the others. We’ve all grown and worked on accepting that our experiences are different without one being more valid than the other. You have to do that when you have eight siblings and are part of a large group,« she says.
Actually, that’s necessary regardless, says Ida Wentzel.
»Sibling relationships today are emotional rather than practical, and it is as vulnerable a relationship as any other. This has become even more evident with the increase in step and half-siblings. The more siblings there are, the more complex siblinghood can be. Yet most people will go to great lengths to hold onto their siblings,« she says.
»It’s hard for us to break free from people who have always been with us.«
Siblings have always been surrounded by myths, prejudices, and what Ida Wentzel calls »homemade opinions« because nearly everyone has their own experiences with the topic. Theories about the impact of birth order on personality have especially dominated discussions.
But according to Ida Wentzel, this has overshadowed more interesting discoveries about siblings.
When she and her colleagues examined the significance of siblings through interviews with 100 siblings, they found it didn’t make sense to categorize siblings based on birth order. Instead, they realized how much siblinghood is constantly in motion.
As children, we are continually developing each other. And as we grow older and head out into the world, it can be crucial whether you live next door to your sister or have moved to China.
»It’s a relationship that is often fluctuating, evolving, and shifting until you die,« says Ida Wentzel.
Success can trickle down through the group
For many years, siblings have been primarily studied within psychology. In recent years, however, researchers in a series of recognized studies have successfully shown significant statistical influences from one sibling to another.
Adam Altmejd, an associate professor at Stockholm University and lead author of the largest of these studies, is an economist. Along with research colleagues from three countries, he has demonstrated spillover effects in sibling choices of education across nations and cultures.
The study compiled data on those who began higher education since 1992 in Sweden, the USA, Chile, and Croatia. It shows that younger siblings are likely to study the same subject at the same institution as their older siblings, and if they can’t get into that particular program, they still have a higher tendency to study something else at the same institution.
»I was very surprised that we could show such a clear sibling effect,« says Adam Altmejd.
The study is considered groundbreaking because it is difficult to demonstrate statistically significant trends in familial relationships, which can also be influenced by genetics and other social relationships. Here, the researchers succeeded in isolating the sibling relationship and questioning whether some choices, currently seen as results of upbringing or parents, might actually be influenced by siblings.
Since the study was published in 2022, several follow-up studies have emerged. A Yale study found that children who are among the oldest in their class when they start school achieve better grades than other children in the same class, even if it’s just a matter of a few months’ age difference. In a sibling context, this is interesting because researchers found that this advantage trickles down to younger siblings, regardless of their age when they start school.
Thus, your school performance partly depends on how old your older siblings were when they started.
Collectively, the discovery of spillover effects among siblings has made researchers curious about whether, for example, improving the living conditions for the eldest sibling could enhance the well-being of the entire sibling group.
Adam Altmejd elaborates.
»Our results show that siblings are important role models and drivers behind educational choices. This means that the conditions for the oldest sibling suddenly become interesting. One could imagine endless forms of political initiatives aimed at improving the circumstances for the eldest, who would hopefully then influence the younger siblings,« he says.
When Dorianne Kristiansen finished her HF (Higher Preparatory Examination), it was somewhat obvious what she should do.
»I started studying to become a teacher because my older sister did,« she says.
She explains that it felt like a natural choice because her sister had already paved the way, and often, she says, you need someone to set the course for you. For ... »then there’s a path you can lean into«.
Dorianne Kristiansen’s father was an engineer, and her mother was trained in banking. However, most of her siblings ended up following in the footsteps of the eldest in the group. Several pursued humanities degrees. She shares that it’s not only in educational choices that they’ve mirrored each other but also in many of life’s other significant decisions.
To some extent, it’s still like that today. When Dorianne Kristiansen has to make a decision, she sometimes thinks:
»What would my siblings think?«.
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