  We analyse the available data on the polarized asymmetries $A_1$ for proton,
neutron and deuteron targets. We use a homogeneous and updated set of
unpolarized structure functions to derive $g_1$ from $A_1$, and we accurately
correct for the scaling violations in order to obtain $g_1(x,Q^2)$ with the
same $Q^2$ for all $x$ values. The contribution to the $Q^2$ evolution of a
possible large gluon polarized density is also considered. The implications for
the Ellis-Jaffe and for the Bjorken sum rules are discussed.
