The hypercharges of the fermions are not uniquely determined in SO(10) grand
unification, but rather depend upon which linear combination of the two U(1)
subgroups of SO(10) > SU(3) X SU(2) X U(1) X U(1) remains unbroken. We show
that, in general, a given hypercharge assignment can be obtained only with very
high-dimensional Higgs representations. The observation that the standard model
is obtained with low-dimensional Higgs representations can therefore be
regarded as further evidence for SO(10) grand unification. This evidence is
independent of the fact that SO(10) > SU(5).Comment: 6 pages, Late
