A new study from researchers at MIT and Northwestern University has found something many families may already suspect — second-born children, especially boys, are more likely to be rebellious and get into trouble than their older siblings.
The research, which looked at data from both the U.S. and Denmark, shows that birth order can play a big role in shaping behavior. While first-borns often take on leadership roles and try to meet their parents’ expectations, their younger brothers are more likely to challenge rules and even end up facing disciplinary issues or legal trouble.
So, what’s behind this rebellious streak? Experts believe it comes down to parenting styles. First-borns usually get more one-on-one attention from their parents, especially in their early years. By the time a second child arrives, parents may be busier or more relaxed, leading to less supervision. Without as much guidance or pressure to behave a certain way, second-born kids may take more risks.
The study doesn’t suggest that all younger siblings are troublemakers — far from it. But it does highlight how family dynamics and parenting differences can shape personality in surprising ways.
This research adds fuel to the long-standing debate about whether birth order really affects who we become. While not everyone agrees, it’s a reminder that our place in the family tree might have more influence than we think.
So next time your younger sibling breaks a rule or pushes boundaries, it might not just be “bad behavior” — it could be science at work.
And if you’re the second-born? Well, maybe you were just born to stand out.
