When Does Natural Selection Determine Evolutionary Direction?

Natural selection is credited for giving direction to evolution. But it is also described as a filter acting on variation supplied by mutation, development and chance. These views highlight different regimes, not rival truths. In this paper, I ask when selection actually determines evolutionary direction. I define determination counterfactually, i.e. an outcome is selection determined if it recurs across replicate histories under the same selective regime and becomes much less likely when selection factor is removed. Here, I argue that four conditions must hold jointly- (i) selection must outweigh drift, (ii) the selective regime must persist, (iii) variation should not be biased enough to overturn selection's ranking and (iv) landscape must allow the favored route to be travelled. Each failure hands direction to a distinct process. Determination also falls as outcomes are described more firmly, from function to phenotype to sequence. Finally, six testable predictions are stated.