Abstract

None of the concepts thus far advanced by biologists or philosophers of life covers in a satisfactory way all instances and aspects of biological individuality. Two main, only partially overlapping notions must be distinguished: physiological individuality, based on morphological or molecular attributes, and evolutionary individuality, based on the uniqueness of the role played by the individual in evolutionary processes. The three individuality criteria suggested by Pradeu, i.e. uniqueness, delineation and persistence, are useful as a rough guide, but their application faces serious problems or limitations, e.g. with polygenomic organisms or polyembryonic metazoans. Persistence of individuality throughout development deserves accurate revisitation.