show Abstracthide AbstractGenetic adaptation is difficult to study in non-model organisms, especially as laboratory experiments are impractical for long-lived species. However, new genomic methods have revealed specific amino acid changes, genes, and biochemical pathways that are repeatedly involved in adaptation to survival in high altitude environments. This study addresses two questions: 1) What is the genetic basis for high-altitude adaptation in Andean hummingbirds? And 2) Are the mechanisms the same across divergent taxa and populations? Studying natural cases of parallel evolution is the key to discovering how predictable evolutionary processes are and the range of possible adaptive paths.