The science of sibling dynamics: Why we fight, how we relate and why it matters

We have Mother’s Day, Father’s Day and even Grandparents’ Day. But siblings? Usually they get a hand-me-down sweatshirt and, with any luck, a lifetime of inside jokes.

But actually, there is a National Siblings Day, observed every April 10. It was founded in 1995 by Claudia Evart in memory of her late siblings, as a reminder to appreciate these relationships while we can. 

About 80% of people have a sibling, and It turns out, there’s a lot to appreciate — research shows that siblings influence far more than just childhood, shaping lifelong social skills and deeply affecting all kinds of relationships.

So, just how important are siblings? What roles do they play throughout life, and how do those roles evolve? In honor of the day, we asked Dan Erickson, associate teaching professor at Arizona State University's T. Denny Sanford School of Social and Family Dynamics and director of ASU’s Certified Family Life Educator program, to discuss.

Editor’s note: Responses have been edited for length and clarity.

Question: Why are sibling relationships sometimes the most enduring but also the most conflict-prone?

Answer: It’s the most enduring because it is typically the longest consistent relationship. Although parents and romantic partners may often have a deeper relationship, siblings typically outlast both, as they are more likely to be present near the beginning and end of life.

Due to the involuntariness of their relationship in childhood, siblings are fully dependent on shared parents for all their needs, which means they have to endure — or celebrate — the presence of the other sibling(s). The close proximal relationship not only provides easy access for aggression, but because siblings are often competing with each other for resources, they often have higher frequencies of conflicts than peers. 

In fact, children and adults often treat their friends better than their siblings because those relationships are fully voluntary. But they know their siblings can’t escape them, which makes it easier to engage in conflict because their sibling can't leave the relationship.

Q: How much sibling conflict is considered normal or healthy?

A: Conflict in sibling relationships is normal, because it’s normal in every relationship, but aggression and violence are not normal. Many parents don’t intercede in sibling aggression because they assume it is normal, but parents have a responsibility to help their children navigate conflict in non-violent ways, including modeling appropriate interpersonal interactions.

In a similar vein, my dissertation showed that how adolescents interact with their siblings, including conflict resolution and warmth, will likely be similar to how they interact as adults in romantic relationships. The adolescent sibling relationship is a powerful sandbox to try out attachment and other relationship behaviors. So unless you want your child to believe that aggression and violence are normal in adult relationships, don’t normalize that behavior in sibling relationships.

Q: How do siblings support each other throughout their lifetime?

A: There is meaningful research showing that in childhood and adolescence, siblings can help each other in unique and powerful ways. For example, siblings with autism often have the best interventions when their similarly aged sibling participates in the intervention. Similarly, in emerging adulthood and later life, siblings have unprecedented opportunities to support each other. A sibling is typically among, if not the very first person that an LGBTQ+ person comes out to, for example. And when facing difficulties, such as health concerns or tragedies, who better than someone who has shared your entire life and who shares your DNA to help get you through it? When parents or family members die, the grief is uniquely shared by siblings. 

So although the parent-child and romantic relationships may be deeper than the typical sibling relationship, people who choose to prioritize the most enduring relationship with their siblings will find deep and lasting joy and connection.

Q: What are the effects of sibling favoritism from parents?

A: Favoritism is a very poignant reality in families. If a parent is being honest, they will likely admit that they have a favorite child — whether consciously or unconsciously. Parents think they can expertly convince their children that they “love all their children equally,” but due to personal differences, even the premise of loving or treating children equally is a fallacy of parenthood — and a simple impossibility. The oldest child in a family, for example, gets an average of 3,000 extra one-on-one hours with their parents.

Comparing children to a sibling, however expertly they think they may be at it, does more damage than good, as it holds children to a standard that may very well be unrealistic. Each human being is unique, and even when children share DNA, they are very different individuals. Rather than focusing on trying to be “equal,” parents would do better to emphasize the unique differences of their children and love them for their differences. When children feel that their parents unequivocally love and accept them for who they are, with no strings attached and no obligations, worries about favoritism become less salient because love is not a resource that needs to be competed for.

Q: What advice would you give to someone trying to reconnect with an estranged sibling?

A: First and foremost, you must acknowledge their sovereign personhood. Just because you share DNA, and even decades of close proximity, you are not entitled to anything more than that person is willing to give. Although estrangement can be heartbreaking, especially if you don’t fully understand why, making judgments of that person or their behavior deepens the rift whether you realize it or not. Above all, do not triangulate the relationship by bringing in another family member to try to “fix” things, because doing so will only lead to further heartache.

Try to communicate clearly with your estranged sibling, unless they have specifically asked for no contact. Communicate your genuine love and respect. If you genuinely love and respect them, it should be easy to go from there, because you will not make selfish or manipulative demands of them. Nevertheless, they are their own person and may make decisions you don’t understand or agree with. So long as they fully understand that you love them, respect them and are open to further interactions, you can sleep soundly at night knowing that if and when they are ready, they will bridge that gap.

Q: How can siblings strengthen their relationship in adulthood?

A: Most people forget to allow other people to change. We get this idea in our head of who people are based on outdated information. Older siblings often remember changing their younger sibling’s diaper, or childish immaturities. But that child should be allowed to grow up and become different, or we are doing them and ourselves a disservice. Respect and love your sibling enough to get to know who they are now.

Older siblings bear more responsibility in setting the tone for adult sibling relationships, as they’ve been adults longer. There is amazing potential in sibling relationships, as they are the most enduring relationship in humanity. It is worth the investment to get to know yourself first, then take the time to get to know your sibling, and if you approach these relationships with an open heart, you may surprise yourself and them with the opportunity to forge deep and meaningful relationships.