  We propose a simple model in which the cosmological dark matter consists of
particles whose mass increases with the scale factor of the universe. The
particle mass is generated by the expectation value of a scalar field which
does not have a stable vacuum state, but which is effectively stabilized by the
rest energy of the ambient particles. As the universe expands, the density of
particles decreases, leading to an increase in the vacuum expectation value of
the scalar (and hence the mass of the particle). The energy density of the
coupled system of variable-mass particles (``vamps'') redshifts more slowly
than that of ordinary matter. Consequently, the age of the universe is larger
than in conventional scenarios.
