  The time evolution of a cosmological scalar field can be stopped by an
increasing mass of the neutrinos. This leads to a transition from a
cosmological scaling solution with dynamical dark energy at early time to a
cosmological constant dominated universe at late time. The trigger for the
transition is set at the time when the neutrinos become non-relativistic. The
characteristic mass scale for dark energy is thus related to the neutrino mass,
the only known particle physics scale in its vicinity. This explains the ``why
now problem'' for dark energy. We present a particle physics realization of
this ``growing matter'' scenario. It is based on the very slowly varying mass
of a superheavy scalar triplet field whose expectation value dominates the
light neutrino masses.
