  Formation and evolution of galaxies have been a central driving force in the
studies of galaxies and cosmology. Recent studies provided a global picture of
cosmic star formation history. However, what drives the evolution of star
formation activities in galaxies has long been a matter of debate. The key
factor of the star formation is the transition of hydrogen from atomic to
molecular state, since the star formation is associated with the molecular
phase. This transition is also strongly coupled with chemical evolution,
because dust grains, i.e., tiny solid particles of heavy elements, play a
critical role in molecular formation. Therefore, a comprehensive understanding
of neutral-molecular gas transition, star formation and chemical enrichment is
necessary to clarify the galaxy formation and evolution. Here we present the
activity of SKA-JP galaxy evolution sub-science working group (subSWG) Our
activity is focused on three epochs: z \sim 0, 1, and z > 3. At z \sim 0, we
try to construct a unified picture of atomic and molecular hydrogen through
nearby galaxies in terms of metallicity and other various ISM properties. Up to
intermediate redshifts z \sim 1, we explore scaling relations including gas and
star formation properties, like the main sequence and the Kennicutt-Schmidt law
of star forming galaxies. To connect the global studies with spatially-resolved
investigations, such relations will be plausibly a viable way. For high
redshift objects, the absorption lines of HI 21-cm line will be a very
promising observable to explore the properties of gas in galaxies. By these
studies, we will surely witness a real revolution in the studies of galaxies by
SKA.
