  Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution
around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield
statistically significant galaxy halo mass measurements over a much wider range
of stellar masses ($10^{8.75}$ to $10^{11.3} M_{\odot}$) and redshifts ($0.2 <
z < 0.8$) than previous weak lensing studies. At redshift $z \sim 0.5$, the
stellar-to-halo mass ratio (SHMR) reaches a maximum of $4.0\pm0.2$ percent as a
function of halo mass at $\sim 10^{12.25} M_{\odot}$. We find, for the first
time from weak lensing alone, evidence for significant evolution in the SHMR:
the peak ratio falls as a function of cosmic time from $4.5 \pm 0.3$ percent at
$z \sim 0.7$ to $3.4 \pm 0.2$ percent at $z \sim 0.3$, and shifts to lower
stellar mass haloes. These evolutionary trends are dominated by red galaxies,
and are consistent with a model in which the stellar mass above which star
formation is quenched "downsizes" with cosmic time. In contrast, the SHMR of
blue, star-forming galaxies is well-fit by a power law that does not evolve
with time. This suggests that blue galaxies form stars at a rate that is
balanced with their dark matter accretion in such a way that they evolve along
the SHMR locus. The redshift dependence of the SHMR can be used to constrain
the evolution of the galaxy population over cosmic time.
