Life sciences · Preprint
arXiv · September 10, 2026
Early or partial results. Treat as a signal, not a conclusion.
This preprint describes a spatial-partitioning variant of ES-HyperNEAT that mitigates a central-bias failure mode on MNIST, achieving 43% mean accuracy versus 21% baseline—a 106% relative improvement. The gain stems from forcing evolved networks to discover features across the entire image (expanding pixel coverage from 4% to 79%), not from weighting aggregation; however, absolute accuracy remains substantially below gradient-trained methods, and the work is limited to a single toy benchmark.
Computational diagnostic and methods development study. MNIST digit classification benchmark; no empirical population studied.. Intervention: 13-expert spatially partitioned ES-HyperNEAT architecture with equal-weighted aggregation. Compared with: Baseline ES-HyperNEAT (single network); gradient-trained methods mentioned as external reference but no direct comparison reported.
Baseline ES-HyperNEAT achieves 21% mean accuracy on MNIST due to spatial-concentration bias at image centre 13-expert spatially partitioned design reaches 43% mean accuracy, a 106% relative improvement over baseline Equal-weighted averaging of experts yields 70% improvement without validation-data-driven aggregation
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This is an early-stage computational study demonstrating a workaround for a known failure mode in neuroevolution on a toy benchmark (MNIST), with no comparison to established neuroevolution baselines and results still well below gradient-trained methods.
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Evolvable-Substrate HyperNEAT (ES-HyperNEAT), a bio-inspired indirect encoding that determines neuron placement and connection weights from spatial coordinates, exhibits a failure mode on MNIST as a diagnostic benchmark. Because input pixels map to a coordinate space centered at the origin, evolved networks converge on a small central cluster of input pixels, a spatial-concentration bias; prior work observed only 21% mean accuracy in this regime. Is this bias an optimization artifact or an architectural ceiling? Inspired by Mixture-of-Experts (MoE) principles, we partition the input into non-overlapping spatial segments, each assigned to a separately evolved specialist network. With 13 such experts, this design reaches 43% mean accuracy, a 106% relative improvement over the baseline. The architectural gain does not depend on data-driven aggregation: equal-weighted averaging, which uses no validation data, already yields a 70% improvement; the gain comes from partitioning, not the weighting. Receptive-field analysis shows the mechanism: partitioning forces evolution to discover features across the entire image, expanding active pixel coverage from 4% to 79%. Absolute accuracy stays below gradient-trained baselines, but the relative gain points to central bias, not the evolutionary search. Two tools are designed to generalize beyond MNIST: a receptive-field diagnostic for silent input-coverage collapse, and a spatial-partitioning remedy that restores coverage.
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