  Following previous work, we further confirm that the cosmic evolution of
steep-spectrum radio-loud AGNs (active galactic nuclei) can be reproduced by a
simple combination of density evolution (DE) and luminosity evolution (LE).
This mixture evolution scenario can naturally explain the luminosity-dependent
evolution of radio-loud AGNs. Our models successfully fitted a large amount of
data on radio luminosity functions (RLFs) of steep-spectrum sources and
multi-frequency source counts. The modeling indicates that the DE slowly
increase as $(1+z)^{0.3 \thicksim 1.3}$ out to $z \thicksim 0.8$, and then
rapidly decreases as $(1+z)^{-6.8 \thicksim -5.7}$, while the LE rapidly
increase as $(1+z)^{4.8}$ out to a higher redshift (at least $z>3.5$). We find
a high-redshift decline (i.e. redshift cutoff) in the number density of
steep-spectrum radio sources, but we cannot conclude whether such decline is
sharp or shallow. We believe that whether a redshift cutoff occurs or not
depends mainly on DE, while its steepness is decided by LE, which, however,
cannot be well constrained due to the lack of high-redshift samples. Most
intriguingly, according to our mixture evolution scenario, there appears to be
no need for different evolution for the low- and high-power radio-loud AGNs.
Both types of sources experience the same combined evolution of DE and LE.
