  A simple phenomenological description for the energy transfer between a
variable cosmological constant (CC) and a gas of relic neutrinos in an
expanding universe can account for a near coincidence between the neutrino and
dark-energy densities to hold over a significant portion of the history of the
universe. Although such a cosmological setup may promote neutrinos to
mass-varying particles, both with slow and quick neutrino mass changing with
the expansion of the universe naturally implemented in the model, it also works
equally well for static neutrino masses. We also stress what sort of models for
variable CC can potentially underpin the above scenario.
