Quark masses and mixing angles in a four-generation model with a naturally heavy neutrino

It is argued with the help of an illustrative model with some interesting predictions that the interspecies hierarchy among the fermion masses and the quark mixing angles can be accommodated naturally in the standard model with approximately equal Yukawa couplings for all the fermions, provided there are four sequential quark-lepton families with all members of the fourth family having roughly equal masses. The special problem of very light neutrino masses (if any) and possible solutions are also discussed. In the quark sector, the model is shown to be consistent with the observed neutral meson mixing data and has a few interesting predictions. It is also shown that the existence of precisely four generations is strongly favored within a wide class of models with a few very reasonable assumptions about naturalness.