Abstract：
Along the evolutionary path from single cells to multicellular organisms with a central nervous system are species of intermediate complexity that move in ways suggesting high-level coordination, yet have none. Instead, organisms of this type possess many autonomous cells endowed with programs that have evolved to achieve concerted responses to environmental stimuli. How does this low-level multicellular organism coordinate its cells to achieve organism-level behaviours? Here experiment and theory are used to develop a quantitative understanding of how cells of such organisms coordinate to achieve phototaxis (swimming towards the light) of the colonial green algae Volvox and we discovered that coordination is achieved by a common cellular response program to environmental stimuli, a precise morphological organization and a mutual 'fine-tuning' of the biochemical time scales with the characteristic spinning frequency of the colony in its viscous physical environment.