though mostly distinct, are related in an incomparably closer degree to
each other than to the inhabitants of any other part of the world. And
this is just what might have been expected on my view, for the islands
are situated so near each other that they would almost certainly
receive immigrants from the same original source, or from each other.
But this dissimilarity between the endemic inhabitants of the islands
may be used as an argument against my views; for it may be asked, how
has it happened in the several islands situated within sight of each
other, having the same geological nature, the same height, climate,
etc., that many of the immigrants should have been differently
modified, though only in a small degree. This long appeared to me a
great difficulty: but it arises in chief part from the deeply-seated
error of considering the physical conditions of a country as the most
important for its inhabitants; whereas it cannot, I think, be disputed
that the nature of the other inhabitants, with which each has to
compete, is at least as important, and generally a far more important
element of success. Now if we look to those inhabitants of the
Galapagos Archipelago which are found in other parts of the world
(laying on one side for the moment the endemic species, which cannot be
here fairly included, as we are considering how they have come to be
modified since their arrival), we find a considerable amount
of difference in the several islands. This difference might indeed have
been expected on the view of the islands having been stocked by
occasional means of transport a seed, for instance, of one plant having
been brought to one island, and that of another plant to another
island. Hence when in former times an immigrant settled on any one or
more of the islands, or when it subsequently spread from one island to
another, it would undoubtedly be exposed to different conditions of
life in the different islands, for it would have to compete with
different sets of organisms: a plant, for instance, would find the
best-fitted ground more perfectly occupied by distinct plants in one
island than in another, and it would be exposed to the attacks of
somewhat different enemies. If then it varied, natural selection would
probably favour different varieties in the different islands. Some
species, however, might spread and yet retain the same character
throughout the group, just as we see on continents some species
spreading widely and remaining the same.
The really surprising fact in this case of the Galapagos Archipelago,
and in a lesser degree in some analogous instances, is that the new
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