In the first part of my talk I will address the question whether the morphology-density relation is instrinsic, or the result of more fundamental, underlying relations between galaxy mass, environment and star formation activity. In the second part I will describe our study of the evolution of the early-type galaxy fraction with redshift based on stellar mass-selected samples of field and cluster galaxies. Selecting galaxies by mass turns out to drastically change the picture with respect to results based on luminosity-selected samples, which are traditionally used for such analyses.