The evolution of self during the transition to multicellularity.

The notion of ' self' is intrinsically linked to the concepts of identity and individuality. During evolutionary transitions in individuality-such as, for instance, during the origin of the first cell, the origin of the eukaryotic cell and the origin of multicellular individuals-new kinds of individuals emerged from the interaction of previously independent entities. The question discussed here is: How can new types of individuals with qualities that cannot be reduced to the properties of their parts be created at a higher level? This question is addressed in the context of the transition to multicellularity and using the volvocine green algae-a group of closely related unicellular and multicellular species with various degrees of physiological and reproductive unity-as a model system. In this chapter, we review our framework to addressing the evolution of individuality during the transition to multicellularity, focusing on the reorganization of general life-traits and cellular processes and the cooption of environmentally-induced responses.