  We show that in see-saw models with bimaximal lepton mixing at the GUT scale
and with zero CP phases, the solar mixing angle theta_{12} generically evolves
towards sizably smaller values due to Renormalization Group effects, whereas
the evolution of theta_{13} and theta_{23} is comparatively small. The
currently favored LMA solution of the solar neutrino problem can thus be
obtained in a natural way from bimaximal mixing at the GUT scale. We present
numerical examples for the evolution of the leptonic mixing angles in the
Standard Model and the MSSM, in which the current best-fit values of the LMA
mixing angles are produced. These include a case where the mass eigenstates
corresponding to the solar mass squared difference have opposite CP parity.
