  We investigate models in which a spectrum of black holes with Hawking
temperature of order the radiation temperature at the beginning of the
radiation dominated era can survive long enough to produce a matter dominated
era at the observed crossover between matter and radiation in our universe. We
find that a sufficiently dense population of such black holes can indeed do so.
The stronger observational constraint, that the black holes have lifetimes at
least as long as the current age of the universe is harder to assess, because
of black hole mergers during the matter dominated era. We then investigate
whether the required densities and masses are consistent with the Holographic
Space-time (HST) model of inflation. We find that they are, but put mild
constraints on the slow roll parameter $\epsilon = - \frac{\dot{H}}{H^2}$ in
that model to be small. The bound is no stronger than the observational bound
on the model's prediction for tensor fluctuations. The required black hole
density, at the reheat temperature, in a model with a single species of black
hole, must be viewed as a quantum mechanical accident. In such a model, our
universe exists because of a low probability quantum fluctuation.
