  We use very deep (R_lim=27) UGRI imaging to study the evolution of the faint
end of the UV-selected galaxy luminosity function from z~4 to z~2. We find that
the number of sub-L* galaxies increases from z~4 to z~3 while the number of
bright ones appears to remain constant. We find no evidence for continued
evolution to lower redshift, z~2. If real, this differential evolution of the
luminosity function suggests that differentially comparing key diagnostics of
dust, stellar populations, etc. as a function of z and L may let us isolate the
key mechanisms that drive galaxy evolution at high redshift and we describe
several such studies currently underway.
