Strengthening the Foundations of Law as Extended Phenotype: Coalitional Intelligence and the Evolutionary Origins of Legal Institutions

Evolutionary legal theory faces a fundamental explanatory gap: why natural selection produced organisms capable of creating, transmitting, and enforcing abstract normative rules. To my knowledge, this paper provides the first integration of the Coalitional Intelligence Hypothesis (CIH) by Egeland, Kennair, and Kleppestø (2026) with Extended Phenotype Theory (EPT) as applied to legal systems, generating a four-stage evolutionary genealogy that neither framework produces independently. The CIH posits that human intelligence evolved as an honest signal of coalitional value, facilitating reciprocal exchanges of prestige for cognitive-computational services (conflict resolution, collective coordination, normative articulation). EPT argues that law operates as the extended phenotype of competing normative memes. The integration proposes that formal legal institutions are memetically codified elaborations of the coalitional value system: proto-jurists provisioning coordination services received prestige in small-scale societies; modern law institutionalizes that exchange through deontic language and specialized structures. The integrated framework generates three falsifiable predictions with specified measurement protocols: (1) legal systems exhibit institutional signatures of coalitional value exchange; (2) professional prestige correlates with cognitive-computational service quality beyond formal credentials; (3) legal transplant failures correlate with coalitional value system mismatches. Boundary conditions are specified determining when CIH versus EPT have greater explanatory leverage, and limitations regarding indirect archaeological evidence and dependence on untested CIH predictions are explicitly acknowledged. The integration provides evolutionary microfoundations for institutional legal theory, with testable implications for institutional design, legal reform, and comparative analysis of legal systems.