| Many of us assign personality traits to the family pecking order: the bossy firstborn, the peacekeeping middle child, and, woe to us all, the reckless youngest. When researchers test such tidy predictions, analyzing the statistical souls of millions of people, they have reached the same conclusion: Birth order has no durable predictive power over your personality. When it comes to foreseeing your future, it’s about as good as astrology. Your rank in the birth lineup can shape your life. It just doesn’t define the unique combination of thoughts, feelings and behaviors that make you who you are. As I’ve written, younger siblings fare worse, on average, than firstborns across a range of metrics, including lifetime earnings and educational achievement. That’s because differences in quality time with parents and, perhaps to a greater degree, serious respiratory infections shape a child’s development in ways that reverberate through the decades. Could there be more? You asked me to dig into it after my previous column on birth order.You were right to ask. Our personality is supposed to be stable. Researchers say that enduring traits known as “The Big Five” best describe our personalities across cultures: extroversion, agreeableness (that’s compassion, respectfulness and trust); conscientiousness (organization and responsibility); neuroticism (anxiety, depression and volatility) and openness to experience (imagination and curiosity). Once we reach adulthood, scientists believed these five factors cohere into a largely permanent “I” with only modest changes thereafter. New personality research is revising those assumptions. Birth order isn’t a serious driver of our enduring personality, says Ted Schwaba, a psychologist and assistant professor at Michigan State University who studies personality development and behavioral genetics. Rather than being fixed in the sky at birth, two decades of research suggests personality is far less static than once believed. “People always retain the capacity to change,” says Schwaba. Our personalities shift — sometimes dramatically — throughout our lifetime in response to personal experiences, deliberate effort or the gentle sanding of years. The majority of people, says Schwaba, see a steady decline in neuroticism, our tendency to experience anxiety, sadness, worry, anger and guilt. “It’s the strongest evidence for any trait change,” says Schwaba, who confesses to anxiety himself, “which is the most reassuring finding in the whole world.” Here’s how scientists believe birth order — and everything else — affects how we act and what really matters when it comes to our personality. | 
