  The redshifts of lens galaxies in known gravitational lens systems probe the
volume distribution of lensing mass. Following earlier work by Kochanek, we
re-derive the lens redshift probability distribution, allowing for mass and
number density evolution of the lensing galaxies, and apply this test to a much
enlarged sample of lens systems. From a literature survey of all known lenses,
we have selected an unbiased sample of 15 lenses with complete redshift
information. For a flat Universe and no lens evolution, we can only put an
upper limit on the cosmological constant of Omega_lambda<0.89 at the 95% CL.
Omega_lambda~0.7 and no evolution is consistent with the data. Allowing for
evolution in an Omega_m=0.3, Omega_lambda=0.7 cosmology, we find that the
best-fit evolution in sigma* (i.e., the characteristic velocity dispersion in a
Schechter-like function) of early-type galaxies, in the redshift range z~0 to
1, is d[log sigma*(z)]/dz=-0.10+/-0.06. This is consistent with no evolution
and implies that, at 95% CL, sigma* of early-type galaxies at z~1 was at least
63% of its current value. Alternatively, if there is no mass evolution, a
present-day value of sigma*>175 km/s for elliptical galaxies is required (95%
CL).
