The Scope of Natural Selection: MITTENS-Validated Case Studies in Local Adaptation

The MITTENS framework (Mathematical Impossibility of The Theory of Evolution by Natural Selection) establishes quantitative constraints on achievable fixations based on generation time, the selective turnover coefficient (d), and empirically observed fixation rates. While MITTENS demonstrates a 158,000-fold shortfall for macro-evolutionary divergence (e.g., human-chimpanzee), critics might argue that local adaptation represents an intermediate test case. Here we examine four well-documented examples of local adaptation: beach mouse pigmentation, stickleback armor reduction, peppered moth melanism, and warfarin resistance in rats. In every case, the required genetic changes involve 1–3 fixations—precisely the scale MITTENS predicts natural selection can accomplish. Using taxon-appropriate parameters and, where available, empirically measured selection coefficients, we show that all four cases pass MITTENS constraints. The peppered moth case is particularly instructive: MITTENS predicts 0.66 achievable fixations, implying the allele should reach high frequency but not fix—exactly what was observed before selection reversed. These results confirm that natural selection operates effectively within its proper scope while remaining incapable of the million-fold extrapolation required for macro-divergence. The boundary is not philosophical; it is mathematical.