Many evolutionary discussions equate fitness with reproductive success. This formulation captures an important part of evolutionary continuity because reproduction contributes to the persistence of living organisation through time. Yet reproduction alone does not explain why continuity occurs.
Living systems persist through the maintenance of viability-oriented organisation distributed across physiology, development, behaviour, and ecological interaction. Reproductive success contributes to future continuity only when this broader organisation remains capable of sustaining persistence across changing conditions.
APS therefore treats reproduction as one contributor to fitness rather than as fitness itself. Fitness concerns the historically situated continuity of persistence-sustaining organisation across generations. Reproduction matters because it helps regenerate continuity, but continuity ultimately depends upon the organisation being reproduced remaining viable under developmental and ecological conditions.
Fitness is therefore not best understood as reproductive output alone. It is better understood as the differential continuity of organised persistence through time.