The article explores why total directional selection and evolutionary responses are limited in natural populations. By analyzing data from over 4,600 estimates of selection, the researchers found that trade-offs among fitness components, correlated selection, and stabilizing selection do not strongly constrain directional selection for most traits. Fluctuations in selection over time have limited impact on cumulative directional selection. Stabilizing selection on body size was observed in some cases, but disruptive selection is more common for most traits.