Description This paper traces the emergence of the proposition "humanity as an end in itself" from individual practice to civilizational institution, constituting the third paper in the SAE Anthropology Series and the most interface-rich paper in the Self-as-an-End framework. 15DD is defined as structural non-doubt that the Other is an end — not moral rule, not ethical argument, but a structural certainty analogous to non-doubt about gravity. The paper distinguishes cognitive-level 15DD (seeing the Other as an end) from saintly 15DD (seeing it and choosing to nurture others at personal cost rather than self-protect or profit). Four independently emerging individuals around 500 BCE — Confucius, Shakyamuni, Socrates, and Jesus — serve as illustrative anchor points (not an exhaustive list). Their near-simultaneous appearance across unconnected civilizations is explained as structural necessity: independent systems under identical constraints produce comparable timelines, with 14DD institutional pressure reaching a critical threshold that forces the choice to nurture. The paper identifies three lines redirected at the 15DD threshold: literature and art (making the Other-as-end perceptible), philosophy (arguing that humans are not means), and exemplar recognition traditions (preserving those who did not doubt the Other's status as end). Literature serves as the primary carrier of 15DD remainder across a 2,300-year germination period from the Axial Age to Kant's 1785 formulation. A two-axis structural criterion governs the four phases: the expansion of the inclusion boundary ("who counts as an end") and the degree of externalization ("lived → displayed → written → institutionalized"). The spectral flip (Kant) is followed by a 200-year acceleration band (abolition, decolonization, civil rights), then institutional crystallization in the League of Nations and United Nations system — identified as the most advanced attempt by a 14DD container to carry a 15DD proposition, not 15DD itself. Key original contributions include: the civilization rebootability hypothesis (15DD remainder must crystallize independently of 14DD institutions to provide cross-regime normative continuity); the ancient Egypt brittleness diagnosis (overly dense institutional structure prevents independent crystallization); the observation that philosophy decelerated after Kant while practice accelerated (structural: without real opposition, conviction drifts); and the antibody effect (institutionalized old 15DD can suppress new 15DD emergence). Three falsifiable predictions are offered. All SAE series converge in this paper. Keywords Self-as-an-End; 15DD; humanity as an end; Axial Age; remainder conservation; phase transition; civilization rebootability; Kant; literature as remainder carrier; United Nations; human rights; institutional crystallization Series SAE Anthropology Series, Paper III Series Predecessors Prequel "The Cosmic Background of Anthropology" (DOI: 10.5281/zenodo.19503158) Paper I "The Emergence of 13DD" (DOI: 10.5281/zenodo.19531334) Paper II "The Emergence of 14DD" (DOI: 10.5281/zenodo.19546082) Language Chinese (primary), English (independent rewrite) License CC BY 4.0 Resource Type Publication — Preprint Related Identifiers SAE Paper 1: DOI 10.5281/zenodo.18528813 (isPartOf) SAE Paper 2: DOI 10.5281/zenodo.18666645 (isPartOf) SAE Paper 3: DOI 10.5281/zenodo.18727327 (isPartOf) Kant Paper: DOI 10.5281/zenodo.18808585 (references) Philosophy History Coordinates: DOI 10.5281/zenodo.18842897 (references) Aesthetics Paper: DOI 10.5281/zenodo.19296710 (references) Methodology Paper VI: DOI 10.5281/zenodo.19464506 (references) Methodology Paper VII: DOI 10.5281/zenodo.19481304 (references) Economics Paper 4: DOI 10.5281/zenodo.19393913 (references) Anthropology Paper I: DOI 10.5281/zenodo.19531334 (isNewVersionOf: series) Anthropology Paper II: DOI 10.5281/zenodo.19546082 (isNewVersionOf: series) Law Series: DOIs 10.5281/zenodo.19548238–19549019 (references) Life/Death Paper 6: DOI 10.5281/zenodo.19528780 (references) Multi-AI Architecture: DOI 10.5281/zenodo.19366105 (references) Learning Series Paper 4: DOI 10.5281/zenodo.19491926 (references) Terrible Teens: DOI 10.5281/zenodo.19201631 (references) Art History Application: DOI 10.5281/zenodo.18775062 (references) Subjects Philosophy; Anthropology; History; Ethics; Political Philosophy; Civilization Studies Notes The English version is an independent rewrite, not a translation. Where nuances diverge, the Chinese text is authoritative. AI language models were used in the writing process. Claude (Anthropic) for structural discussion, outline development, draft iteration, and language editing. ChatGPT (OpenAI) for deep research literature survey. ChatGPT, Gemini (Google), and Grok (xAI) for outline and manuscript review. All theoretical content, conceptual innovations, normative judgments, and analytical conclusions are the independent work of the author.