Fermion masses and mixings from higher dimensions

A systematic discussion of the structure of fermion mass matrices in terms of quantum numbers is presented. Small ratios between fermion masses and small mixing angles are related to a fine structure of scales around the unification scale. We argue that in higher dimensional models all small fermion masses should be explained from symmetry considerations since no free small Yukawa couplings are available. This leads to a scanning procedure selecting higher dimensional models consistent with realistic fermion mass patterns. (orig.)