  Deep surveys conducted during the past decades have shown that galaxies in
the distant universe are generally of more irregular shapes, and are disky in
appearance and in their star formation rate, compared to galaxies in similar
environments in the nearby universe. Given that the merger rate between z=2 and
the local universe is far from adequate to account for this observed
morphological transformation rate, an internal mechanism for the morphological
transformation of galaxies is to be sought, whose operation can be further
aided by environmental factors. The secular evolution mechanism, especially
with the discovery of a collisionless dissipation mechanism for stars within
the secular evolution paradigm, has provided just such a framework for
understanding the morphological evolution of galaxies across the Hubble time.
In this paper we will summarize the past theoretical results on the dynamical
mechanisms for secular evolution, and highlight new results in the analysis of
the observational data, which confirmed that density waves in physical galaxies
possess the kind of characteristics which could produce the observed rates of
morphological transformation for both cluster and field galaxies.
