Affective Socialization Theory (AST) bridges neuroscience, psychology, and sociology to explain how human behaviors are structurally patterned by society rather than individually chosen. This first paper introduces the biological mechanism of Affective Myelination, detailing how transient childhood emotions stretch into durable moods, which ultimately lock into a foundational neural baseline during the critical developmental phase of Affective Consolidation (traditionally identified as the development of metacognition). Depending on the environment, this baseline wires the individual for specific forms of Agency Expectancy (Collective, Commodified, or Predatory) or forces a shutdown state where no agency is expressed. These individual adaptations then aggregate across populations to form the overarching Hegemonic Mood Climate (HMC) of a society. While the adult brain retains neuroplasticity, rewiring these deeply ingrained pathways requires a significant material rupture and sustained Socialization Exposure Doses (SED') within enabling environments. However, if the Material Strain Index (MAT) exceeds a critical threshold, the nervous system locks into a survival state, rendering neuro-affective rehabilitation impossible without prior structural relief. Ultimately, this paper establishes the biological foundations of AST, defines the primary individual and emergent context variables, and introduces the mathematical framework for the AST recursive loop.