  We revisit the scale evolution of the quark and gluon spin contributions to
the proton spin, $\frac{1}{2}\Delta \Sigma$ and $\Delta G$, using the
three-loop results for the spin-dependent evolution kernels available in the
literature. We argue that the evolution of the quark spin contribution may
actually be extended to four-loop order, and that to all orders a single
anomalous dimension governs the evolution of both $\Delta \Sigma$ and $\Delta
G$. We present analytical solutions of the evolution equations for $\Delta
\Sigma$ and $\Delta G$ and investigate their scale dependence both to large and
down to lower "hadronic" scales. We find that the solutions remain
perturbatively stable even to low scales, where they come closer to simple
quark model expectations. We discuss a curious scenario for the proton spin, in
which even the gluon spin contribution is essentially scale independent and has
a finite asymptotic value as the scale becomes large. We finally also show that
perturbative three-loop evolution leads to a larger spin contribution of
strange anti-quarks than of strange quarks.
