or the shape of their intrinsic dynamical structure. The possibility that evolution in any of these quantities may in fact occur has left the interpretation of FP studies somewhat uncertain. This possibility has come into sharp focus through the fact that the inferred $M/L$ evolution of massive early-type galaxies is well fit by models of passive evolution following formation at high redshift, and by the fact that there appears to be only a small age difference between massive early-type galaxies in clusters and the field (vDvdM06). Although models can be constructed that reproduce these results (e.g., Nagamine [[et al. ]{}]{}2005; De Lucia [[et al. ]{}]{}2006), they do appear somewhat counter-intuitive given the paradigm of hierarchical structure formation in the Universe. Moreover, there exist sophisticated semi-analytical models in which the evolution of galaxy $M/L$ and FP zeropoint are actually quite different (Almeida, Baugh & Lacey 2006). So there are many reasons to critically question whether FP evolution does in fact uniquely trace $M/L$ evolution.

The most direct way to address this question is to determine $M/L$ values for individual distant galaxies in the same way as has been done locally, without resorting to FP assumptions. This requires construction of detailed dynamical 