  We construct a dynamical model for the parton distributions in a nucleus by
perturbative evolution of input distributions from a low starting scale. These
input distributions are obtained by modifications of the corresponding free
nucleon ones; the modifications being determined by standard nuclear physics
considerations. The model gives good agreement with existing data. Its
extension to the spin dependent case enables an estimation of nuclear
modifications to asymmetries observed in recent doubly polarised deep inelastic
scattering experiments. Although the structure functions themselves are very
different from the free nucleon ones, their ratio is insensitive to these
changes.
