  It is now a well established fact that galaxies undergo significant
morphological transformation during their lifetimes, manifesting as an
evolution along the Hubble sequence from the late to the early Hubble types.
The physical processes commonly believed to be responsible for this observed
evolution trend, i.e. the major and minor mergers, as well as gas accretion
under a barred potential, though demonstrated applicability to selected types
of galaxies, on the whole have failed to reproduce the most important
statistical and internal properties of galaxies. The secular evolution
mechanism reviewed in this paper has the potential to overcome most of the
known difficulties of the existing theories to provide a natural and coherent
explanation of the properties of present day as well as high-redshift galaxies.
