  Deep surveys in the far-infrared and sub-millimeter wavebands are revealing a
new phase of galactic evolution hidden by dust. Observations with SCUBA on the
JCMT show that 25% of the COBE/FIRAS background at 850 microns is being
produced by high luminosity sources (L ~ 3x10^12 L_sun) at high redshifts 0.5 <
z < 3+. These sources have an estimated redshift distribution that is broadly
consistent with a global star-formation history that is similar to that
inferred from optical observations. The sub-mm galaxies and optically selected
galaxies are producing comparable quantities of stars. However, the sub-mm
sources are doing so in systems that have luminosities that are an order of
magnitude higher, and comoving densities an order of magnitude lower, then the
optically selected galaxies. These high luminosity sources are plausibly
responsible for producing the spheroidal components of massive galaxies at z ~
2.
