Validation: Physiology
Frasch (2026a). Causal thinking in physiology — A search for vertically organising principles. The Journal of Physiology, DOI 10.1113/JP290762.
The claim
Modern physiology has worked horizontally for a century: within molecular, cellular, tissue, organ, and organism scales, mechanism is identified by within-scale interventions. Vertically organising principles — laws that connect scales — have remained elusive. NWAP is proposed as a candidate: a single action functional whose extrema are scale-invariant, predicting modularity as the architectural substrate of multi-scale integration.
Method
A theoretical synthesis of three lineages:
- The scaling tradition from Kleiber's law to West et al.'s fractal geometry of metabolic networks.
- Noble's principle of biological relativity, which establishes bidirectional causation between scales.
- The dynamic-coordination tradition (Schöner & Kelso, Tognoli & Kelso) that already formalises energy-driven coordination of weakly coupled non-linear oscillators.
NWAP is the action whose Euler–Lagrange equations recover the dynamic-coordination phase equation as a special case.
The result
The framework reproduces three established empirical regularities — Kleiber's $3/4$ scaling, Noble's bidirectional causation, and the modularity of biological networks (Clune et al. 2013) — from a single action principle, without per-scale modelling. "Meaning", operationally defined as successful uncertainty reduction through efficient action, emerges at the intersection of free-energy and dissipative-adaptation accounts.
What this domain adds to the programme
It establishes the framework formally, provides the unifying schema (Figure 1 of the paper, panels A–E), and shows that NWAP is consistent with every existing major variational account in physiology. It is the theoretical anchor of the four-domain programme.
Figure 1 from Frasch 2026a (J Physiol, DOI: 10.1113/JP290762, CC BY). Panels A–E: horizontal vs vertical causality (A); life at the edge of chaos (B); the Network-Weighted Action across scales (C); emergence of modularity from cost minimisation (D); convergence of theoretical frameworks with "meaning" at the centre (E).