The origin and persistence of biological complexity present one of the deepest explanatory challenges in science. This paper develops the biological applications of Relational Actualism (RA), a foundational physics framework in which irreversible on-shell actualization events are the primitive physical reality. Building on the five foundational theorems proved in the companion paper RAHC---the Assembly Index Correspondence, the DAG Markov Property, the Markov Blanket Isomorphism, the Landauer Cost of Actualization, and the Epistemic-Physical Equivalence bound---this paper establishes: (1) the Actualism Assembly Index as a physically grounded measure of biological causal depth, supported by a B3LYP/6-311+G* density functional survey across the five primary bond types of life; (2) the Causal Firewall as the physical phase transition that separates abiotic chemistry from stable biological complexity; (3) the thermodynamic grounding of natural selection as simultaneous optimization of causal assembly depth, edge-of-chaos operation, and Markov blanket fidelity; and (4) the categorical impossibility of Boltzmann Brains. Five empirical predictions follow, spanning astrobiology, origin-of-life chemistry, evolutionary biology, and the universal search for life. A new result: the Causal Firewall threshold σ = λτdℓ³ = 1 is proved (not merely conjectured) via the directed Erdős-Rényi percolation theorem applied to the Poisson-CSG causal graph, identifying the Firewall with the onset of a giant strongly connected component and universal causal ledger agreement.
Joshua Sandeman (Thu,) studied this question.