  Our knowledge of the blazar surface densities and luminosity functions, which
are fundamental parameters, relies still on samples at relatively high flux
limits. As a result, our understanding of this rare class of active galactic
nuclei is mostly based on relatively bright and intrinsically luminous sources.
We present the radio number counts, evolutionary properties, and luminosity
functions of the faintest blazar sample with basically complete (~ 95%)
identifications. Based on the Deep X-ray Radio Blazar Survey (DXRBS), it
includes 129 flat-spectrum radio quasars (FSRQ) and 24 BL Lacs down to a 5 GHz
flux and power ~ 50 mJy and ~ 10^{24} W/Hz, respectively, an order of magnitude
improvement as compared to previously published (radio-selected) blazar
samples. DXRBS FSRQ are seen to evolve strongly, up to redshift ~ 1.5, above
which high-power sources show a decline in their comoving space density. DXRBS
BL Lacs, on the other hand, do not evolve. High-energy (HBL) and low-energy
(LBL) peaked BL Lacs share the same lack of cosmological evolution, which is at
variance with some previous results. The observed luminosity functions are in
good agreement with the predictions of unified schemes, with FSRQ getting close
to their expected minimum power. Despite the fact that the large majority of
our blazars are FSRQ, BL Lacs are intrinsically ~ 50 times more numerous.
Finally, the relative numbers of HBL and LBL in the radio and X-ray bands are
different from those predicted by the so-called "blazar sequence" and support a
scenario in which HBL represent a small minority (~ 10%) of all BL Lacs.
