  We assume that strong and electroweak interactions become strong at very high
energies. With this assumption, we compute the low-energy gauge coupling
constants $\alpha_i (m_Z)$ as a function of the cutoff scale, taking the
supersymmetric standard model with $3+2n$ families of quark and lepton
multiplets. We find that only the five family case $(n=1)$ is consistent with
the experimental values of the gauge coupling constants. This suggests the
presence of a pair of families at $\sim 1$~TeV.
