  Observations have evidenced that passively evolving massive galaxies at high
redshift are much more compact than local galaxies with the same stellar mass.
We argue that the observed strong evolution in size is directly related to the
quasar feedback, which removes huge amounts of cold gas from the central
regions in a Salpeter time, inducing an expansion of the stellar distribution.
The new equilibrium configuration, with a size increased by a factor >~ 3, is
attained after ~ 40 dynamical times, corresponding to ~ 2 Gyr. This means that
massive galaxies observed at z >~ 1 will settle on the Fundamental Plane by z ~
0.8-1. In less massive galaxies (M_star <~ 2 10^10 M_sun), the nuclear feedback
is subdominant, and the mass loss is mainly due to stellar winds. In this case,
the mass loss timescale is longer than the dynamical time and results in
adiabatic expansion that may increase the effective radius by a factor of up to
~ 2 in 10 Gyr, although a growth by a factor of ~ 1.6 occurs within the first
0.5 Gyr. Since observations are focused on relatively old galaxies, with ages
>~ 1 Gyr, the evolution for smaller galaxies is more difficult to perceive.
Significant evolution of velocity dispersion is predicted for both small and
large galaxies.
