When I had read Charles Darwin's book 'On the Origin of Species,' it
seemed to me that there was one mode, and that perhaps the most certain,
of testing the correctness of the views developed in it, namely, to
attempt apply them as specially as possible to some particular group of
animals. such an attempt to establish a genealogical tree, whether for
the families of a class, the genera of a large family, or for the
species of an extensive genus, and to produce pictures as complete and
intelligible as possible of the common ancestors of the various smaller
and larger circles, might furnish a result in three different ways.

1. In the first place, Darwin's suppositions when thus applied might
lead to irreconcilable and contradictory conclusions, from which the
erroneousness of the suppositions might be inferred. If Darwin's
opinions are false, it was to be expected that contradictions would
accompany their detailed application at every step, and that these, by
their cumulative force, would entirely destroy the suppositions from
which they proceeded, even though the deductions derived from each
particular case might possess little of the unconditional nature of
mathematical proof.

2. Secondly, the attempt might be successful to a greater or less
extent. If it was possible upon the foundation and with the aid of the
Darwinian theory, to show in what sequence the various smaller and
larger circles had separated from the common fundamental form and from
each other, in what sequence they had acquired the peculiarities which
now characterise them, and what transformations they had undergone in
the lapse of ages,--if the establishment of such a genealogical tree, of
a primitive history of the group under consideration, free from internal
contradictions, was possible,--then this conception, the more completely
it took up all the species within itself, and the more deeply it enabled