  The main energy-generating mechanisms in galaxies are black hole (BH)
accretion and star formation (SF) and the interplay of these processes is
driving the evolution of galaxies. MIR/FIR spectroscopy are able to distinguish
between BH accretion and SF, as it was shown in the past by infrared
spectroscopy from the space by the Infrared Space Observatory and Spitzer.
Spitzer and Herschel spectroscopy together can trace the AGN and the SF
components in galaxies, with extinction free lines, almost only in the local
Universe, except for a few distant objects. One of the major goals of the study
of galaxy evolution is to understand the history of the luminosity source of
galaxies along cosmic time. This goal can be achieved with far-IR spectroscopic
cosmological surveys. SPICA in combination with ground based large single dish
submillimeter telescopes, such as CCAT, will offer a unique opportunity to do
this. We use galaxy evolution models linked to the observed MIR-FIR counts
(including Herschel) to predict the number of sources and their IR lines
fluxes, as derived from observations of local galaxies. A shallow survey in an
area of 0.5 square degrees, with a typical integration time of 1 hour per
pointing, will be able to detect thousands of galaxies in at least three
emission lines, using SAFARI, the far-IR spectrometer onboard of SPICA.
