  We show that nuclear interactions are SU(4) symmetric at leading order in
chiral perturbation theory in the large-N limit of QCD. The nucleons and delta
resonances form a 20-dimensional representation of SU(4) and we show how
Wigner's supermultiplet symmetry SU(4)_{sm}, under which the nucleons transform
as a 4-dimensional representation, follows as an accidental low energy
symmetry. Exploiting SU(4) symmetry allows one to express the 18 independent
leading nucleon, delta interaction operators invariant under spin and isospin
symmetries in terms of only two couplings. The three flavor analogue allows one
to express the 28 leading octet, decuplet interactions also in terms of only
two couplings, which has implications for hypernuclei and strangeness in
``neutron'' stars.
