  A combination of evidence is presented suggesting that the majority of the
stars in today's galaxies were born during a luminous infrared phase (LIRP)
triggered by the local environment of galaxies. The CIRB is a fossil record of
these LIRPs and therefore reflects the influence of triggered star formation
through galaxy-galaxy interactions, including non merging tidal encounters.
This scenario, in which galaxies experienced several LIRPs in their history, is
consistent with the measured redshift evolution of the cosmic density of star
formation rates and of stellar masses of galaxies.
