There is enormous variation in lifespan across the tree of life, raising the question of what enables some species to live longer than others. To live a long life, individuals must be able to defend themselves against pathogens over prolonged time periods whilst minimising damage to themselves. The vertebrate immune system is broadly divided into two parts: adaptive and innate immunity. Innate immunity is relatively non-specific, resulting in collateral damage to hosts, and lacks long-term immunological memory. In contrast, adaptive immunity is highly specific and confers long-lasting memory, features predicted to facilitate long life. However, there has never been an explicit test of whether adaptive immunity promotes the evolution of longer life. I plan to address this deficit by testing whether there have been gene family expansions in the adaptive relative to the innate immune system in long-lived compared to short-lived bird species. I plan to use whole genome assemblies from bird species that represent a broad range of lifespans in order to characterise the repertoire of adaptive versus innate immune genes and test the prediction that longer-lived species have experienced an expansion of adaptive relative to innate immune genes.