  The Zoo Hypothesis posits that we have not detected extraterrestrial
intelligences (ETIs) because they deliberately prevent us from detecting them.
While a valid solution to Fermi's Paradox, it is not particularly amenable to
rigorous scientific analysis, as it implicitly assumes a great deal about the
sociological structure of a plurality of civilisations. Any attempt to assess
its worth must begin with its most basic assumption - that ETIs share a
uniformity of motive in shielding Earth from extraterrestrial contact. This
motive is often presumed to be generated by the influence of the first
civilisation to arrive in the Galaxy. I show that recent work on inter-arrival
time analysis, while necessary, is insufficient to assess the validity of the
Zoo Hypothesis (and its related variants). The finite speed of light prevents
an early civilisation from exerting immediate cultural influence over a later
civilisation if they are sufficiently distant. I show that if civilisation
arrival times and spatial locations are completely uncorrelated, this strictly
prevents the establishment of total hegemony throughout the Galaxy. I finish by
presenting similar results derived from more realistic Monte Carlo Realisation
simulations (where arrival time and spatial locations are partially
correlated). These also show that total hegemony is typically broken, even when
the total population of civilisations remains low. In the terminology of
previous studies of solutions to Fermi's Paradox, this confirms the Zoo
Hypothesis as a "soft" solution. However, an important question to be resolved
by future work is the extent to which many separate hegemonies are established,
and to what extent this affects the Zoo Hypothesis.
