  While the Sersic profile family provide adequate fits for the surface
brightness profiles of observed galaxies, the physical origin is unknown. We
show that, if the cosmological density field are seeded by random gaussian
fluctuations, as in the standard cold dark matter model, galaxies with steep
central profiles have simultaneously extended envelopes of shallow profiles in
the outskirts, whereas galaxies with shallow central profiles are accompanied
by steep density profiles in the outskirts. These properties are in accord with
those of the Sersic profile family. Moreover, galaxies with steep central
profiles form their central regions in smaller denser subunits that possibly
merge subsequently, which naturally leads to formation of bulges. In contrast,
galaxies with shallow central profiles form their central regions in a coherent
fashion without significant substructure, a necessary condition for disk galaxy
formation. Thus, the scenario is self-consistent with respect to the
correlation between observed galaxy morphology and Sersic index. We predict
further that clusters of galaxies should display a similar trend, which should
be verifiable observationally.
