The Resistance Capacity Variable: A Developmental Mechanism for Sex Differences in the Psychological Consequences of Adverse Childhood Experiences

The psychological consequences of adverse childhood experiences (ACEs) show consistent sex differences: females exhibit greater internalizing outcomes, while males display more externalizing trajectories. Despite extensive documentation, the generative mechanism underlying this divergence remains underspecified. This paper proposes the Resistance Capacity Variable (RCV), defined as the physical capacity of a maltreated child to resist the perpetrator, operationalized as a continuous variable driven by pubertal musculoskeletal development. RCV is conceptually distinct from secondary sexual maturation (e.g., menarche, breast development), constituting a separate axis of pubertal change. When RCV crosses a threshold—typically during male puberty—the experience of maltreatment is encoded as a deficit of power, promoting externalized self-formation. When the threshold is not reached—as is typical for females and late-maturing males—maltreatment is encoded as an inherent danger of relationships, producing Defensive Self-Formation (DSF). This hypothesis is triangulated through four evidence streams: age-by-sex crossover patterns in national maltreatment victimization data, longitudinal studies of late-maturing males as a natural experiment, large-scale cohort evidence that ACEs accelerate female puberty along the sexual-maturation axis but not the musculoskeletal axis, and intergenerational findings that protective relationships operate only through the physically dominant caregiver. The paper further introduces the concept of Zero-Risk Warmth (ZRW) to explain why AI companions may offer particular psychological value to individuals with DSF. Implications for developmental theory, clinical screening, and the regulation of AI companionship are discussed.