  We have used the available samples of Gigahertz Peaked Spectrum (GPS)
galaxies to investigate their evolution properties in the framework of the
``youth'' scenario. Care was taken to properly allow for the different
selection criteria used to define the samples. We find that the observed
redshift and peak frequency distributions can be satisfactorily accounted for
in terms of simple luminosity evolution of individual sources, along the lines
discussed by Fanti et al. (1995) and Begelman (1996, 1999), although the
derived parameter values have large uncertainties due to ambiguities in the
selection of GPS sources and to the incompleteness of redshift measurements.
However the simplest self-similar model, whereby the evolution is controlled
only by the radial profile of the density of the ambient medium is not good
enough and one additional parameter needs to be introduced. The fit requires a
decrease of the emitted power and of the peak luminosity with source age or
with decreasing peak frequency, at variance with the Snellen et al. (2000)
model. On the other hand, our analysis confirms the rather flat slope of the
luminosity function, found by Snellen et al. (2000) who also report indications
of a high luminosity break, not required by the data sets we have used. Our
results suggest that the GPS galaxies are the precursors of extended radio
sources with luminosities below the break of the luminosity function. No
cosmological evolution of the GPS galaxy population is required by presently
available data.
