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 } \approx 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 \sim 0 to 1 , is d \log { [ \sigma _ { * } ( z ) ] } / dz = -0.10 \pm 0.06 .
This is consistent with no evolution and implies that , at 95 \% CL , \sigma _ { * } of early-type galaxies at z \sim 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 ^ { -1 } 
for elliptical galaxies is required ( 95 \% CL ) .