A simple model is presented for the parton distributions in hadrons. The
parton momenta in the hadron rest frame are derived from a spherically
symmetric, Gaussian, distribution having a width motivated by the Heisenberg
uncertainty relation applied to the hadron size. Valence quarks and gluons
originate from the `bare' hadron, while sea partons arise mainly from pions in
hadronic fluctuations. Starting from a low Q^2 scale, the distributions are
evolved with next-to-leading order DGLAP and give the proton structure function
F2(x,Q^2) in good agreement with deep inelastic scattering data.Comment: 12 pages, Latex, 5 figures. Added discussion on the applicability of
the model at small Q^2. Figure 3 modified to show smaller Q^