  We present a simple model of the infra-red universe, based as much as
possible on local observations. We model the luminosity and number evolution of
disk and starburst galaxies, including the effects of dust, gas and spectral
evolution. Although simple, our approach is able to reproduce observations of
galaxy number counts and the infra-red and sub-millimeter extra-galactic
backgrounds. It provides a useful probe of galaxy formation and evolution out
to high redshift. The model demonstrates the significant role of the starburst
population and predicts high star formation rates at redshifts 3 to 4,
consistent with recent extinction-corrected observations of Lyman break
galaxies. Starbursting galaxies are predicted to dominate the current SCUBA
surveys. Their star formation is driven predominantly by strong tidal
interactions and mergers of galaxies. This leads to the creation of spheroidal
stellar systems, which may act as the seeds for disk formation as gas infalls.
We predict the present-day baryonic mass in bulges and halos is comparable to
that in disks. From observations of the extra-galactic background, the model
predicts that the vast majority of star formation in the Universe occurs at
z<5.
