  The recent high statistics NMC data on the Tin to Carbon structure function
ratio seems to indicate, for the first time, a significant $Q^2$ dependence,
especially at small values of Bjorken $x$, $x < 0.05$, and $Q^2 > 1 GeV^2$.
Pure leading twist, perturbative QCD--based predictions, which are consistent
with the free nucleon data, yield a fairly flat ratio with little or no $Q^2$
dependence. In view of this seeming contradiction, we re-examine the
applicability of such a perturbative model to nuclear structure functions in
such a kinematical regime. We find that the model is consistent with all data,
within experimental errors, without any need for introducing additional higher
twist contributions. The model correctly reproduces the $Q^2$ dependence of the
Carbon structure function as well. We also critically examine the $Q^2$
dependence of the corresponding spin dependent structure functions.
