  We analyze the physical justification of the picture proposed by
Salvador-Sole et al. in these proceedings for the time evolution of the
universal density profile of dark-matter halos. According to this picture,
halos have at formation a stable (i.e. independent of mass and time)
dimensionless density profile, the characteristic length and density scales of
the profile depending on the underlying cosmogony. Subsequent evolution is
driven by mass accretion onto the outskirts of halos and can be characterized
simply by the increment of halo radius with time and the corresponding decrease
of the critical density of the universe. We find this picture to be a
reasonable good description of the expected evolution of halos in hierarchical
models of structure formation.
