102 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
events in large part, derive their inhabitants from accidental or occa- 
sional arrivals of wind-blown or water-floated organisms from other 
countries—especially, of course, from the countries least remote. But, 
after agreeing upon this point, the two theories must part company in 
their anticipations. The special-creation theory can have no reason 
to suppose that a small volcanic island in the midst of a great ocean 
should be chosen as the theatre of any extraordinary creative activity, 
or for any particularly rich manufacture of peculiar species to be 
found nowhere else in the world. On the other hand, the evolution 
theory would expect to find that such habitats are stocked with more 
or less peculiar species. For it would expect that when any organisms 
chanced to reach a wholly isolated refuge of this kind, their descendants 
should forthwith have started upon an independent course of evolu- 
tionary history. Protected from intercrossing with any members of 
their parent species elsewhere, and exposed to considerable changes in 
their conditions of life, it would indeed be fatal to the general theory 
of evolution if these descendants, during the course of many genera- 
tions, were not to undergo appreciable change. It has happened on 
two or three occasions that European rats have been accidentally 
imported by ships upon some of these islands, and even already it is 
observed that their descendants have undergone a slight change of 
appearance, so as to constitute them what naturalists call local 
varieties. The change, of course, is but slight, because the time 
allowed for it has been so short. But the longer the time that a 
colony of a species is thus completely isolated under changed condi- 
tions of life the greater, according to the evolution theory, should 
we expect the change to become. Therefore, in all cases where we 
happen to know, from independent evidence of a geological kind, that 
an oceanic island is of very ancient formation, the evolution theory 
would expect to encounter a great wealth of peculiar species. On the 
other hand, as I have just observed, the special-creation theory can 
have no reason to suppose that there should be any correlation 
between the age of an oceanic island and the number of peculiar species 
which it may be found to contain. 
Therefore, having considered the principles of geographical distri- 
bution from the widest or most general point of view, we shall pass to 
the opposite extreme, and consider exhaustively, or in the utmost 
possible detail, the facts of such distribution where the conditions are 
best suited to this purpose—that is, as I have already said, upon 
oceanic islands, which may be metaphorically regarded as having been 
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