  Fermi's Paradox is the contradiction between the fact that it would seem to
be highly probable that there are other technologically advanced species beyond
the Earth, and the fact that there is no generally accepted evidence for their
existence. Hanson and Bostrom have proposed that there may be a Great Filter, a
survival challenge so lethal that it prevents virtually all species from
evolving to an advanced stage. This paper argues that the Great Filter would be
not one single factor, but rather simply the statistics of survival in an
always-dangerous universe. The frequency of species that survive multiple
existential threats would likely obey a power law such as Lotka's Law, such
that the frequency of survivors would diminish as an inverse power of the
number of threats. Since any species that advances to the point at which it is
detectable on an interstellar scale likely must survive a large number of
existential threats, by Lotka's Law the number of such survivors would be a
very small fraction of the candidate species that evolve on various planets.
Some sobering implications of this picture are outlined.
