Regime interiority and the structural conditions for natural selection.

The organizational closure tradition in theoretical biology holds that self-maintaining organization must precede natural selection, while the Darwinian population framework characterizes how populations vary in their evolutionary character. If closure must precede natural selection, then selection-based explanation has structural prerequisites that can be present or absent. Existing frameworks do not provide a diagnostic for whether those prerequisites hold in a given system. This paper develops such a diagnostic. A null condition specifies system dynamics in the absence of the structural prerequisites for selection, and three criteria, reversibility of organizational roles (R), retention of constraint across transitions (M), and perturbability of organized response (P), diagnose when selection-based explanation applies and whether the conditions under which it operates are themselves sustained. The framework is illustrated using Wrangel Island mammoths and modern cheetahs, two populations with comparable genetic depletion but different structural outcomes. The regime interiority framework identifies a diagnostic distinction that existing approaches do not specify.