The Convergence Index: The Mixing Zone of Human Mechanization and AI Humanization
Bioethics has debated human enhancement (prosthetics, brain-computer interfaces, cognitive offloading), charting the progressive mechanization of body and mind, while AI ethics has examined AI humanization: robotic embodiment, emotional simulation, legal personhood. These two traditions have developed in isolation. This paper argues that the two trajectories converge along a single axis rather than running parallel, and proposes the Convergence Index (CI) for measuring their mutual approach. CI is defined as CI = 1 − |FRR − AIHR|, where the Functional Residual Ratio (FRR) captures the degree to which a human remains non-mechanized, and the AI Humanization Rate (AIHR) captures the degree to which an AI system approximates human capacities. Four measurement dimensions are identified: body, brain/processing, cognition, and mind/affect. A critical finding is that on the body axis, FRR and AIHR share identical engineering metrics: the gait naturalness of a bionic leg and that of a humanoid robot are evaluated by the same biomechanical standards. As CI approaches a Convergence Threshold (CT), the ontological distinction between human and AI becomes empirically unverifiable, a condition formalized by the HYC Theorem (Hatokaze-Yamada-Claude Theorem). Because CT is in principle indeterminate, binary regulatory frameworks are structurally inadequate; gradation-based institutional design becomes unavoidable. Quantitative operationalization is deferred to subsequent research.