  I present an argument, based on the topology of the universe, why there are
three generations of fermions. The argument implies a preferred unified gauge
group of SU(5), but with SO(10) representations of the fermions. The breaking
pattern $SU(5) \to SU(3) \times SU(2) \times U(1)$ is preferred over the
pattern $SU(5) \to SU(4) \times U(1)$. On the basis of the argument one expects
an asymmetry in the microwave data, which might have been detected already.
