10. Development and Aging Proceed in Parallel Rather than Successively

Development is a directed, programmed process of construction and maturation that builds the organismal structure, function, and other elements of its operating architecture; aging is the concurrent accumulation of deleteriome, produced by the same ongoing processes that build and enable function. Development sets the initial conditions and constraints, while aging reflects the default drift of the system being constructed and maintained over time. While many developmental processes are completed by early adulthood, some developmental processes proceed through the entire lifespan. Developmental tempo, aging burden, and aging tempo are therefore distinct but interacting quantities, and developmental processes may shape where age-related drift occurs.