Why are there three generations of fermions in the standard model?
  We show that by decomposing the gauge fields in fermion degrees of freedom and by saturating the remaining degrees of freedom as dynamical fields in the Lagrangian one might explain the proliferation of fermion states in the standard model Lagrangian. Thus the mere presence of the gauge symmetry $U(1)_Y \times SU(2)_L \times SU(3)_c$ is essential. 
Amir H. Fariborz, Renata Jora, Joseph Schechter
hep-ph