Structurally Conditioned Diffusion Reproduces Skills-Based Stratification

Abstract: Occupational hierarchies remain strikingly stable even as job content changes rapidly. We ask whether skill requirements propagate directionally along the wage hierarchy or follow symmetric diffusion. Using O*NET 2015-2024, we analyze 17.3 million directed diffusion opportunities linking 873 occupations and 161 skills. We show that propagation obeys an Asymmetric Trajectory Channeling (ATC) rule: the same requirement spreads differently upward and downward, and the asymmetry depends on skill domain and on the architecture of skill dependencies. Two mechanisms generate ATC. Directional incorporation asymmetry implies that wage gradients create distinct receiving environments: upward-moving socio-cognitive requirements encounter complementary infrastructure, whereas upward-moving sensory/physical requirements face structural indifference. Structural portability constraints imply that dependency position governs portability: requirements anchoring long prerequisite chains carry co-adoption burdens that restrict diffusion regardless of destination. Consistent with these mechanisms, socio-cognitive requirements propagate upward more often than downward (20.7% vs 14.9%), while sensory/physical requirements exhibit the mirror pattern (19.5% downward vs 10.3% upward). Nestedness amplifies these asymmetries in opposite directions: scaffolding capabilities ascend most readily, whereas structurally embedded physical requirements are most tightly confined. Identification leverages within-occupation variation in propagation direction, and results are robust to origin- and destination-side specifications. Together, these findings reveal a directional architecture of occupational change that can reproduce hierarchy through ongoing reconfiguration, even absent assortative preferences or coordinated action.