Photo courtesy of Michael Donovan/The Licensing Project

Maybe you’re the responsible oldest child who acts as a role model for the rest of the family. Or the youngest of several siblings, like me, who enjoys the freedom that comes with your parents’ relaxed rules.

The order in which you were born into your family says a lot about your personality, according to a theory developed by researcher Frank Sulloway, PhD. Sulloway’s niche differentiation theory suggests that while every family dynamic is different, birth order differences are typically influenced by two factors: sibling competition and parental investment. We spoke with professor and psychologist Catherine Salmon, PhD, and therapist Camille Tenerife, LMFT, to help us break down each birth order.

THE FIRSTBORN

Firstborns are the parents’ guinea pigs. With no other siblings around to share the spotlight, the firstborn child receives the whole share of parents’ time and attention, which typically leads the eldest child to become responsible, obedient, and conscientious. Once younger siblings enter the picture, the firstborn might adopt a pseudo-parent role. As the de facto leader of the pack, they often develop a dominant, independent personality and strive to achieve—especially in school and the workplace.

THE MIDDLE CHILD

Each child following the firstborn must develop their own niche that differentiates themselves from their siblings and that garners their parents’ attention.

“The middle child can often feel lost in the shuffle in a sense, and they can get less attention than their siblings,” Salmon says. Their positioning in the center of the family makes them great negotiators and peacekeepers. Though they are typically adaptable, generous, and easygoing, the middle child often feels the need to compete with their siblings for their parents’ attention. This can lead them to resort to rebellious behavior as a means of gaining attention, as well as finding their identity through their relationships with friends and peers.

THE YOUNGEST

By the time they reach their youngest, parents know the drill. They are more confident in their abilities to raise a child, so their approach with the youngest is often more relaxed and lenient. The youngest child tends to evade responsibility. They’re coddled more than their older siblings. Known for being charismatic, outgoing, free-spirited, mischievous, and attention-seeking, the youngest is up for an adventure and willing to take a risk.

THE ONLY CHILD

The only child is raised in a unique household: With no siblings around, they don’t have to worry about sharing clothes, space, or their parents’ attention. Tenerife says, “They may be more rigid and grow up faster because they’re hanging out with a lot of adults.” Like long-term firstborns, only children are the primary recipients of their parents’ support and energy—making them independent, mature, and stubborn.