Biological causation is often described in terms of “bottom-up” processes (component interactions) and “top-down” processes (system-level constraint). APS treats this distinction as a difference in analytic perspective, not as a division between competing causal forces.
Living systems are organised such that the activity of components both enables and is constrained by the organisation they collectively sustain. Molecular interactions realise biological processes, while system-level organisation defines the conditions under which those interactions are viable and meaningful. These are not separate directions of causation but aspects of a single, integrated organisation.
APS therefore understands causation as organisation-dependent and scale-coupled. What appears as bottom-up or top-down reflects how the system is described, not how causation is fundamentally structured.
Causation in biology is not directional but reciprocal: components and organisation co-constitute one another in sustaining viable systems.