  The possibility to violate baryon or lepton number without introducing any
new flavor structures, beyond those needed to account for the known fermion
masses and mixings, is analyzed. With four generations, but only three colors,
this minimality requirement is shown to lead to baryon number conservation, up
to negligible dimension-18 operators. In a supersymmetric context, this same
minimality principle allows only superpotential terms with an even number of
flavored superfields, hence effectively enforces R-parity both within the MSSM
and in a GUT context.
