The Margin–Variance Selector: A Phase Model of Architectural Survival Under Constraint

This paper introduces a domain-agnostic selector geometry governing architectural survival across biological, financial, institutional, and geopolitical systems. The model formalizes two orthogonal constraints: normalized distance from survival margin and effective environmental variance relative to system response time. A minimal survival model demonstrates that architectural breadth is selected as a function of these variables, producing a phase boundary separating specialization and generalism regimes. Under limiting assumptions, the framework collapses to established results including evolutionary bet-hedging, the Kelly criterion, Ashby’s Law of Requisite Variety, and portfolio diversification. The model extends into domains lacking formal selectors, including institutional rigidity, alliance formation, adversarial security systems, and large-scale historical collapse. The framework operates as a constraint geometry rather than a predictive behavioral theory and functions as a subordinate selector within the broader Planetary Convexity research program.