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What Makes You Who You Are?

A new book explores the enduring mysteries of human development.


Does a toddler’s personality predict how she’ll behave as an adult? Does teenage rebellion portend a life of crime? Psychologists and long-time research collaborators Jay Belsky, Avshalom Caspi, Terrie Moffitt, and Richie Poulton explore these questions and other enduring mysteries of human development in their new book, The Origins of You. PT asked the authors to share which developmental factors they believe are the most underappreciated.

1. Randomness

All of us can point to random events that played a pivotal role in life, such as meeting a mentor who redirects a career or surviving a disaster. But it’s hard to register the impact of such incidents. “How do you measure randomness when doing developmental science?” Belsky asks. “I don’t think we know.”

2. Early Traits

It’s difficult to know if early bad behavior—like tantrums or delinquency—should be dismissed or addressed. But data suggests that youthful maladaptive traits may predict adult challenges. “Early behavioral and personality signs may not forecast specific outcomes, but they can foretell general directions,” Caspi says.

3. Historical Changes

Each generation is firmly rooted in its own time and thus may overlook vast shifts throughout history, such as the eradication of major diseases. “Differences among age groups in developmental outcomes may well be caused by their exposure to different environments in early life,” Moffitt says.

4. The Cost of Resilience

Resilient individuals are better able to navigate hardship, Belsky notes. “In the face of adversity, they're blessed." But when it comes to supportive interventions, the highly resilient don't benefit as much as others.