Cosmotopological relation for a unified field theory

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 early universe microwave data, which might have been detected already.