  The Pauli exclusion principle is advocated for constructing the proton and
neutron deep inelastic structure functions in terms of Fermi-Dirac
distributions that we parametrize with very few parameters. It allows a fair
description of the recent NMC data on $F^p_2(x,Q^2)$ and $F^n_2(x,Q^2)$ at
$Q^2=4 GeV^2$, as well as the CCFR neutrino data at $Q^2=3$ and $5 GeV^2$. We
also make some reasonable and simple assumptions to relate unpolarized and
polarized quark parton distributions and we obtain, with no additional free
parameters, the spin dependent structure functions $xg^p_1(x,Q^2)$ and
$xg^n_1(x,Q^2)$. Using the correct $Q^2$ evolution, we have checked that they
are in excellent agreement with the very recent SMC proton data at $Q^2=10
GeV^2$ and the SLAC neutron data at $Q^2=2 GeV^2$.
