We consider here several properties of phonological stress systems, including the midpoint pathology, an unattested pattern in which stress is confined to a word-medial syllable in short words but reverts to an edge-based window in longer words. Previous attempts have been made to rule out midpoint systems by eliminating the phonological constraints that yield them, or by alluding to difficulties in learning them. We suggest that a preference for representing word edges in memory and limits on subitization—evolutionarily older “fossil” abilities which are neither specific to humans nor to language—are sufficient to rule out the midpoint pathology. We take the same approach to motivate accentual window size and some left-right asymmetries observed in the typology of attested stress systems. This approach highlights the relevance of descent in accounting for human cognition, as well as the benefits that evolutionary thinking can bring to the study of language.