nd they often occur in different countries, or
are found fossil in different formations.... We thus see how
difficult it is to determine in every case whether a given
relation is an analogy or an affinity, for it is evident that as
we go back along the parallel or divergent series, towards the
common antetype, the analogy which existed between the two groups
becomes an affinity.... Again, if we consider that we have only
the fragments of this vast system, the stems and main branches
being represented by extinct species of which we have no
knowledge, while a vast mass of limbs and boughs and minute twigs
and scattered leaves is what we have to place in order, and
determine the true position each originally occupied with regard
to the others, the whole difficulty of the true Natural System of
classification becomes apparent to us.

We shall thus find ourselves obliged to reject all those systems
of classification which arrange species or groups in circles, as
well as those which fix a definite number for the division of each
group.... We have ... never been able to find a case in which the
circle has been closed by a direct affinity. In most cases a
palpable analogy has been substituted, in others the affinity is
very obscure or altogether doubtful....

If we now consider the geographical distribution of animals and
plants upon the earth, we shall find all the facts beautifully in
accordance with, and readily explained by, the present hypothesis.
A country having species, genera, and whole families peculiar to
it will be the necessary result of its having been isolated for a
long period, sufficient for many series of species to have been
created on the type of pre-existing ones, which, as well as many
of the earlier-formed species, have become extinct, and made the
groups appear isolated....

Such phenomena as are exhibited by the Galapagos Islands, which
contain little groups of plants and animals peculiar to
themselves, but most nearly allied to those of South America, have
not hitherto received any, even a conjectural explanation. The
Galapagos are a volcanic group of high antiquity and have probably
never been more closely connected with the continent than they are
at present.

He then proceeds at some length to explain how the Galapagos must have
been at first "peopled .