The development of the recognition of self-like individuals, including relatives and conspecifics, often relies on critical experience with parents, siblings, and other predictable referents during early life. For example, in birds, exposure to conspecifics in the nest reliably cues species-recognition for flocking and mating. How then so brood parasitic birds, that lay their eggs in other species' nest, develop conspecific referents when raised by foster parents? And how do hosts recognize and reject foreign eggs and chicks in the nest if they have not yet laid a clutch before? The presenterï¿½s research focuses on the experimental analysis of self-recognition in both parasites and hosts through phenotypic manipulation of the available cues for species recognition during development. The results reveal how a long-hypothesized mechanism, namely self-referenced phenotype matching, enables the evolution of brood parasitism in birds, and perhaps contributes to the ecological flexibility of recognition systems under socially unpredictable conditions in general.