  We consider the cosmological dynamics of a scalar field in a potential with
multiple troughs and peaks. We show that the dynamics of the scalar field will
evolve from light dark matter-like behaviour (such as that of a light axion) to
a combination of heavy dark matter-like and dark energy-like behaviour. We
discuss the phenomenology of such a model, explaining how it can give rise to
the cosmological constant, as well as how it can decouple the dark sector
densities between the time of recombination and today, for both the homogeneous
background and perturbations. The final form of the dark matter is axion-like,
but with abundance and primordial isocurvature modes taking very different
values from traditional, axionic, dark matter.
