  The availability of high-quality spectra for a large number of galaxies in
the SDSS survey allows for a more sophisticated extraction of information about
their stellar populations than, e.g., the luminosity weighted age. Indeed,
sophisticated and robust techniques to fully analyze galaxy spectra have now
reached enough maturity as to trust their results and findings. By
reconstructing the star formation and metallicity history of galaxies from the
SDSS fossil record and analyzing how it relates to its environment, we have
learned how to classify galaxies: to first order the evolution of a galaxy is
determined by its present stellar mass, which in turn seems to be governed by
the merger rate of dark halos.
