  Increasingly good statistical data on the galaxy population at high and low
redshift enable the development of new phenomenological approaches to galaxy
evolution based on application of the simplest continuity equations. This has
given new insights into the different ways in which star-formation in galaxies
is quenched, the role of merging in the population, and into the control of
star-formation in star-forming galaxies and the links between this and chemical
evolution, in particular the existence of SFR as a second parameter in the
mass-metallicity relation. The continuity approach provides a self-consistent
view of the evolving population and exposes linkages between different aspects
of galaxy evolution.
