  Are the morphologies of galaxies imprinted during an early and rapid
formation epoch or are they due to environmental processes that subsequently
transform galaxies between morphological classes? Recent numerical simulations
demonstrate that the cluster environment can change the morphology of galaxies,
even at a couple of cluster virial radii. The gravitational and hydrodynamical
mechanisms that could perform such transformations were proposed in the 1970's,
before the key observational evidence for environmental dependencies - the
morphology-density relation and the Butcher-Oemler effect.
