  At this point in time, there is very little empirical evidence on the
likelihood of a space-faring species originating in the biosphere of a
habitable world. However, there is a tension between the expectation that such
a probability is relatively high (given our own origins on Earth), and the lack
of any basis for believing the Solar System has ever been visited by an
extraterrestrial colonization effort. This paper seeks to place upper limits on
the probability of an interstellar civilization arising on a habitable planet
in its stellar system, using a percolation model to simulate the progress of
such a hypothetical civilization's colonization efforts in the local Solar
neighborhood. To be as realistic as possible, the actual physical positions and
characteristics of all stars within 40 parsecs of the Solar System are used as
possible colony sites in the percolation process. If an interstellar
civilization is very likely to have such colonization programs, and they can
travel over large distances, then the upper bound on the likelihood of such a
species arising per habitable world is on the order of $10^{-3}$; on the other
hand, if civilizations are not prone to colonize their neighbors, or do not
travel very far, then the upper limiting probability is much larger, even of
order one.
