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certain facts that these have probably 1859 1860 1861 1866
their present manner of distribution, that they have 1869 1872

intercommunication. 1859 1860 1866 1869
inter-communication. 1861
intercommunication. Undoubtedly, if one species has any advantage over another, it will in a very brief time wholly or in part supplant it; but if both are equally well fitted for their own places, both will probably hold their separate places for almost any length of time. 1872

are distinct on each; 1859 1860 1861 1866 1869
differ on the different islands; 1872

mocking-thrush 1859 1860 1861 1866 1872
mocking thrush of 1869

there 1859 1860 1861 1866
and young birds hatched, 1869 1872

species, both
of those
those
found in other parts of the world and
of those
those
confined to the archipelago, are common to the several
islands;
islands,
and we may infer from certain facts that these have probably spread from
some
some
one island to the others. But we often take, I think, an erroneous view of the probability of
closely allied
closely-allied
species invading each
other's
others
territory, when put into free intercommunication.
Undoubtedly,
Undoubtedly
if one species has any advantage
whatever
whatever
over another, it will in a very brief time wholly or in part supplant it; but if both are equally well fitted for their own
places,
places
in nature,
in nature,
both probably will hold their
own
own
places and keep separate for almost any length of time. Being familiar with the fact that many species, naturalised through
man's
mans
agency, have spread with astonishing rapidity over
wide areas,
new countries,
we are apt to infer that most species would thus spread; but we should remember that the
species
forms
which become naturalised in new countries are not generally closely allied to the aboriginal inhabitants, but are very distinct
forms,
species,
belonging in a large proportion of cases, as shown by Alph. de Candolle, to distinct genera. In the Galapagos Archipelago, many even of the birds, though so well adapted for flying from island to island, are distinct on each; thus there are three closely-allied species of mocking-thrush, each confined to its own island. Now let us suppose the mocking-thrush
of
of
Chatham Island to be blown to Charles Island, which has its own
mocking-thrush;
mocking-thrush:
why should it succeed in establishing itself there? We may safely infer that Charles Island is well stocked with its own species, for annually more eggs are laid there than can possibly be reared; and we may infer that the mocking-thrush peculiar to Charles Island is at least as well fitted for its home as is the species peculiar to Chatham Island. Sir C. Lyell and Mr. Wollaston have communicated to me a remarkable fact bearing on this