  We exploit a recent advance in the study of topological superconductors to
propose a solution to the family puzzle of particle physics in the context of
SO(18) (or more correctly, Spin(18)) grand unification. We argue that Yukawa
couplings of intermediate strength may allow the mirror matter and extra
families to decouple at arbitrarily high energies. As was clear from the
existing literature, we have to go beyond the Higgs mechanism in order to solve
the family puzzle. A pattern of symmetry breaking which results in the SU(5)
grand unified theory with horizontal or family symmetry USp(4) = Spin(5) (or
more loosely, SO(5)) leaves exactly three light families of matter and seems
particularly appealing. We comment briefly on an alternative scheme involving
discrete non-abelian family symmetries. In a few lengthy appendices we review
some of the pertinent condensed matter theory.
