Development influences evolution not merely by translating genes into phenotypes. It actively channels evolutionary trajectories, mediates environmental interactions, and generates phenotypic variation in structured ways. This chapter explores how developmental processes bias variant production, how developmental plasticity enables organisms to construct and modify their selective environments, and how perturbations during critical windows can have cascading effects across generations. Drawing on evidence from experimental evolution, placental genomics, and mechanical morphogenesis, we discuss how development is a dynamic participant in evolutionary change, whose mechanisms transcend simple error replication narratives. We examine how recently evolved structures like the human brain may be particularly vulnerable to developmental decanalization and how understanding developmental dynamics provides new insights into the origins of complex disorders. This perspective reveals evolution as emerging from the interplay between developmental systems and environments, where genetic information is not merely transmitted but actively interpreted through developmental processes.