Perturbative NLO and NNLO QCD evolutions of parton distributions are studied,
in particular in the (very) small-x region, where they are in very good
agreement with all recent precision measurements of F_2^p(x,Q^2). These
predictions turn out to be also rather insensitive to the specific choice of
the factorization scheme (MS or DIS). A characteristic feature of perturbative
QCD evolutions is a positive curvature of F_2^p which increases as x decreases.
This perturbatively stable prediction provides a sensitive test of the range of
validity of perturbative QCD.Comment: 4 pages, 3 figures, to appear in the Proceedings of the XVth
International Workshop on Deep Inelastic Scattering (DIS07), Munich, Germany,
April 16-20 200
