  We investigate the evolution of mass-selected early-type field galaxies using
a sample of 28 gravitational lenses spanning the redshift range 0 < z < 1.
Based on the redshift-dependent intercept of the fundamental plane in the rest
frame B band, we measure an evolution rate of d log (M/L)_B / dz = -0.56 +/-
0.04 (all errors are 1 sigma unless noted) if we directly compare to the local
intercept measured from the Coma cluster. Re-fitting the local intercept helps
minimize potential systematic errors, and yields an evolution rate of d log
(M/L)_B / dz = -0.54 +/- 0.09. An evolution analysis of properly-corrected
aperture mass-to-light ratios (defined by the lensed image separations) is
closely related to the Faber-Jackson relation. In rest frame B band we find an
evolution rate of d log (M/L)_B / dz = -0.41 +/- 0.21, a present-day
characteristic magnitude of M_{*0} = -19.70 + 5 log h +/- 0.29 (assuming a
characteristic velocity dispersion of sigma_{DM*} = 225 km/s), and a
Faber-Jackson slope of gamma_{FJ} = 3.29 +/- 0.58. The measured evolution rates
favor old stellar populations (mean formation redshift z_f > 1.8 at 2 sigma
confidence for a Salpeter initial mass function and a flat Omega_m =0.3
cosmology) among early-type field galaxies, and argue against significant
episodes of star formation at z < 1.
