  We present an updated phenomenological galaxy evolution model to fit the
Spitzer 24, 70 and 160 microns number counts as well as all the previous mid
and far infrared observations. Only a minor change of the co-moving luminosity
density distribution in the previous model (Lagache, Dole, Puget 2003),
combined with a slight modification of the starburst template spectra mainly
between 12 and 30 microns, are required to fit all the data available. We show
that the peak in the MIPS 24 micron counts is dominated by galaxies with
redshift between 1 and 2, with a non negligible contribution from the z>2
galaxies (~30% at S=0.2 mJy). The very close agreement between the model and
number counts at 15 and 24 microns strikingly implies that (1) the PAHs
(Policyclic Aromatic Hydrocarbons) features remain prominent in the redshift
band 0.5 to 2.5 and (2) the IR energy output has to be dominated by ~3 10^11 Lo
to ~3 10^12 Lo galaxies from redshift 0.5 to 2.5. Combining Spitzer with the
Infrared Space Observatory (ISO) deep cosmological surveys gives for the first
time an unbiased view of the infrared Universe from z=0 to z=2.5.
