  We present a simple and natural way to derive the observed small, positive
cosmological constant from the gravitational interaction of condensing
fermions. In the Riemann-Cartan spacetime, torsion gives rise to the
axial-axial four-fermion interaction term in the Dirac Lagrangian for spinor
fields. We show that this nonlinear term acts like a cosmological constant if
these fields have a nonzero vacuum expectation value. For quark fields in QCD,
such a torsion-induced cosmological constant is positive and its energy scale
is only about 8 times larger than the observed value. Adding leptons to this
picture could lower this scale to the observed value.
