  Elliptical and S0 galaxies dominate the galaxy population in nearby rich
clusters such as Coma. Studies of the evolution of the colors, M/L ratios, and
line indices of early-type galaxies indicate that they have been a highly
homogeneous, slowly evolving population over the last ~65% of the age of the
Universe. On the other hand, recent evidence suggests that many early-type
galaxies in clusters have been transformed from spiral galaxies since z~1.
Arguably the most spectacular evidence for such transformations is the
incidence of red merger systems in several high redshift clusters. Due to this
morphological evolution the sample of early-type galaxies at high redshift is
only a subsample of the sample of early-type galaxies at low redshift. This
``progenitor bias'' results in an overestimate of the mean formation redshift
if simple models without morphological transformations are used. Models which
incorporate morphological evolution explicitly can bring the homogeneity, slow
evolution, and morphological transformations into agreement. The modeling shows
that the corrected mean formation redshift of the stars in early-type galaxies
may be as low as z~2 in a Lambda dominated Universe.
