Development

Change across a life.

Childhood

Attachment, language acquisition and cognitive stages are the classic areas. Development is more continuous and more variable than stage theories originally suggested.

Early experience matters and rarely determines outcomes on its own.
Adolescent brain development continues into the mid twenties.

Nature and nurture

Genes and environment interact constantly: genes shape which environments you seek, and environments alter which genes are expressed. The percentage framing was always misleading.