  The parton distributions in the proton are evaluated dynamically using a
nonlinear QCD evolution equation - the DGLAP equation with twist-4 (the
GLR-MQ-ZSR) corrections - starting from a low scale $\mu^2$, where the nucleon
consists of valence quarks. We find that the negative nonlinear corrections can
improve the perturbative stability of the QCD evolution equation at low $Q^2$.
Our resulting parton distributions of the proton with four free parameters are
compatible with the existing databases.
  We show that the sea quark distributions exhibit a positive and flattish
behavior at small $x$ and low $Q^2$. This approach provides a powerful tool to
connect the quark models of the hadron and various non-perturbative effects on
them at scale $\mu^2$ with the measured structure functions at high scale
$Q^2>> \mu^2$.
