We compare the evolution with cosmic time of the star formation rate per co
moving volume in galaxies and of the volume emissivity due to active galact
ic nuclei, in an attempt to understand the relationship between black hole
accretion and the formation of the surrounding structure. We find an intere
sting similarity between the evolution rates for the total populations of g
alaxies and AGN, which indicates that, on average, the history of black hol
e accretion follows that of stellar formation in the host galaxies. Similar
ly, the evolution of luminous quasars parallels that of the stellar populat
ions in massive spheroidal galaxies, in keeping with the locally establishe
d association of supermassive black holes and galactic bulges. We finally c
omment on our finding that high-luminosity, high-mass systems evolve on a s
horter cosmic time-scale than lower mass ones; to explain this, theories of
structure formation based on the gravitational collapse of dark matter hal
oes must be complemented with a detailed description of the dynamical proce
sses in the baryonic component, which dominate the formation and evolution
in high-density environments.