 Recall the trait question: Why do zebras have stripes? Devitt (2008, 352ff.) argues that explanations that merely cite relations are insufficient to explain the traits typically found among zebras. We must cite intrinsic properties as well, and such properties are essential intrinsic properties of zebras. Devitt is right that we need to cite more than relations to explain why zebras have stripes. Generally, to explain the occurrence of a homologue, such as stripes in zebras, we need to cite both relations among organisms and intrinsic factors within organisms. More precisely, embryonic zebras have developmental mechanisms that cause zebras to have stripes. These mechanisms are intrinsic features of embryonic zebras. But those developmental mechanisms must be passed down from parent to offspring, via genealogical relations. So a robust explanation of why zebras have stripes cites both the relations and intrinsic properties that cause stripes.