Residual-Space Evolutionary Optimization via Flow-based Generative Models

Data editing with generative methods typically requires differentiable objectives and gradient-based search. However, these assumptions break down in flow-based settings, where edits are performed through forward and backward integration and often involve non-differentiable or black-box objectives. We introduce residual-space evolutionary optimization, a model-agnostic framework that addresses this gap by combining flow-based generative editing with evolutionary algorithms. Building on the observation that conditional flow matching (CFM) can disentangle condition-controlled factors from instance-specific residuals, our framework directly operates in residual space and separates two complementary search regimes: Self-pollination performs local exploitation through feature-preserving residual refinement. Cross-pollination promotes broader exploration by recombining residuals across heterogeneous samples. As a proof of concept, we validate the framework on MorphoMNIST, a benchmark dataset for counterfactual generation, and on crystal data. The results demonstrate that this exploration--exploitation decomposition provides a useful mechanism for balancing target alignment, instance preservation, and diversity, while extending beyond images to real-world scientific domains.