  We review the perturbative evolution of the polarized structure functions g_1
and their associated parton distribution functions, with particular emphasis on
the anomalous coupling of the first moment of the polarized gluon distribution.
We also describe the small x behaviour of polarized parton distributions,
contrasting it with that of the unpolarized distributions. We then explain how
this theoretical analysis affects the extraction of the singlet axial charge
from experimental data on g_1, and show that it may be possible to use such
data to infer the existence of polarized gluons in the nucleon.
