…[S]ystems biology is the study of the behavior of complex biological organization and processes in terms of the molecular constituents. It is built of molecular biology in its special concern for information transfer, on physiology for its special concern with adaptive states of the cell and organism, on developmental biology for the importance of defining a succession of physiological states in that process, and on evolutionary biology and ecology for the appreciation that all aspects of the organism are products of selection, a selection we rarely understand on a molecular level. Systems biology attempts all of this through quantitative measurement, modeling, reconstruction, and theory. Systems biology is not a branch of physics but differs from physics in that the primary task is to understand how biology generates variation. … [T]he success of systems biology is essential if we are to understand life; its success is far from assured – a good field for those seeking risk and adventure.