Dynamical effects on galaxies in clusters
  The observed morphological evolution since z ~ 0.5 within galaxy clusters provides evidence for a hierarchical universe. This evolution is driven by dynamical effects that operate within the cluster environment -- suppression of star-formation by ram-pressure and viscous stripping of the intra-galactic medium and tidal heating of disks by gravitational encounters. 
Ben Moore, Vicent Quilis, Richard Bower