ompete, is as 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 {401} 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 species
formed in the separate islands have not quickly spread to the other
islands. But the islands, though in sight of each other, are separated by
deep arms of the sea, in most cases wider than the British Channel, and
there is no reason to suppose that they have at any former period been
continuously united. The currents of the sea are rapid and sweep across the
archipelago, and gales of wind are extraordinarily rare; so that the
islands are far more effectually separated from each other than they appear
to be on a map. Nevertheless a good many {402} species, both those found in
other parts of the world and those confined to the archipelago, are common
to the several islands, and we may infer from certain facts that these have
probably spread from some one island to the others. But we often take, I
think, an erroneous view of the probability of cl