Blood as a Redox-Suspended Regulatory System

Why are blood groups discrete rather than continuous? Blood circulation presents an extreme biochemical constraint: oxygen, catalytic metals, and reactive metabolites must be transported continuously under flow without permitting irreversible redox completion. While the molecular basis of blood group antigens is well characterised, existing explanations focus primarily on immune self–non-self recognition and do not address why only a small number of discrete surface states persist, nor why incompatibility reactions are abrupt and catastrophic. This preprint reframes blood as a redox-suspended regulatory system evolved to distribute oxidative potential while preventing chemical completion under continuous circulation. Within this constraint space, only a limited number of membrane glycosylation end-states remain inert, non-aggregating, and redox-safe under flow, producing discrete blood group stability attractors rather than continuous variation. The framework further integrates mammalian reproduction, proposing that egg encapsulation, placental buffering, and postnatal immune calibration represent sequential expressions of the same compatibility regime. Immune reactions are interpreted as secondary enforcement mechanisms that rapidly eliminate configurations permitting runaway aggregation or redox escalation. The model generates testable predictions across species with differing placental invasiveness and gestational strategies and offers a unifying physical explanation for blood group discreteness, circulatory fragility, and reproductive interface stability. This work is presented as a theoretical preprint intended to invite critical evaluation and empirical testing.