  We consider the habitability of Earth-analogs around stars of different
masses, which is regulated by the stellar lifetime, stellar wind-induced
atmospheric erosion, and biologically active ultraviolet (UV) irradiance. By
estimating the timescales associated with each of these processes, we show that
they collectively impose limits on the habitability of Earth-analogs. We
conclude that planets orbiting most M-dwarfs are not likely to host life, and
that the highest probability of complex biospheres is for planets around K- and
G-type stars. Our analysis suggests that the current existence of life near the
Sun is slightly unusual, but not significantly anomalous.
