For decades, developmental psychologist Jay Belsky has focused on one of the biggest questions in human development: how do early experiences shape the lives we go on to live?

In this conversation with Michael Shermer, he explains why childhood adversity can leave deep marks, why some children are far more affected by experience than others, and why averages often hide the most important part of the story. Belsky revisits the old nature-versus-nurture debate, but pushes past the usual framing. His argument is not that childhood determines everything in some simple, uniform way. It's that children differ in how developmentally "plastic" they are. The same divorce, the same stress, the same family conflict, or the same support can have very different effects depending on the child.

The discussion moves through attachment theory, father absence, family conflict, puberty, epigenetics, and the evolutionary logic of development.

Belsky also returns to one of his central ideas: the children who are most vulnerable under harsh conditions may also be the ones most likely to flourish when conditions improve. That insight has major implications for how we think about parenting, intervention, and social policy.

Jay Belsky is a developmental psychologist and one of the field's most influential and highly cited researchers. Over a four-decade career at Penn State, the University of London, and UC Davis, he studied how early-life experience shapes attachment, family relationships, and child development. His new book is The Nature of Nurture: Rethinking How Childhood Adversity Shapes Development.