  The standard theoretical estimation of the thermal dark matter abundance may
be significantly altered if properties of dark matter particles in the early
universe and at the present cosmological epoch differ. This may happen if,
e.g., a cosmological phase existed in the early universe during which dark
matter particles were temporarily unstable and their abundance was reduced
through their decays. We argue that a large class of microscopic theories which
are rejected due to the dark matter overproduction, may actually be viable
theories if certain macroscopic conditions were satisfied in the early
universe. We explicitly demonstrate our mechanism within the minimal
supersymmetric standard model with the bino-like lightest supersymmetric
particle being a phenomenologically viable dark matter candidate under the
condition that the early universe carried a global R-charge which induced the
instability phase.
