Arkani-Hamed and Schmaltz (AS) have shown that proton stability need not
originate from symmetries in a high energy theory. Instead the proton decay
rate is suppressed if quarks and leptons are spatially separated in a compact
extra dimension. This separation may be achieved by coupling five dimensional
fermions to a bulk scalar field with a non-trivial vacuum profile and requires
relationships between the associated quark and lepton Yukawa couplings. We
hypothesise that these relationships are the manifestation of an underlying
symmetry. We further show that the AS proposal may suggest that proton
stability \emph{is} the result of an underlying symmetry, though not
necessarily the traditional baryon number symmetry.Comment: 4 pages, references added to match published versio