  We analyze the evolution of the Fundamental Plane for 141 field spheroidal
galaxies in the redshift range 0.2<z<1.2, selected morphologically to a
magnitude limit F850LP=22.43 in the northern field of the Great Observatories
Origin Survey. For massive galaxies we find that the bulk of the star formation
was completed prior to z=2. However, for the lower mass galaxies, the
luminosity-weighted ages are significantly younger. The differential change in
mass-to-light ratio correlates closely with rest-frame color, consistent with
recent star formation and associated growth. Our data are consistent with mass
rather than environment governing the overall growth, contrary to the
expectations of hierarchical assembly. We discuss how feedback, conduction, and
galaxy interactions may explain the downsizing trends seen within our large
sample.
