same Order, 'Primates'; and if there were any animals more like men
than they were like any of the apes, and yet different from men in
important and constant particulars of their organization, we should
rank them as members of the same Family, or of the same Genus, but as of
distinct Species.

That it is possible to arrange all the varied forms of animals into
groups, having this sort of singular subordination one to the other, is
a very remarkable circumstance; but, as Mr. Darwin remarks, this is a
result which is quite to be expected, if the principles which he lays
down be correct. Take the case of the races which are known to be
produced by the operation of atavism and variability, and the
conditions of existence which check and modify these tendencies. Take
the case of the pigeons that I brought before you; there it was shown
that they might be all classed as belonging to some one of five
principal divisions, and that within these divisions other subordinate
groups might be formed. The members of these groups are related to one
another in just the same way as the genera of a family, and the groups
themselves as the families of an order, or the orders of a class; while
all have the same sort of structural relations with the wild
rock-pigeon, as the members of any great natural group have with a real
or imaginary typical form. Now, we know that all varieties of pigeons
of every kind have arisen by a process of selective breeding from a
common stock, the rock-pigeon; hence, you see, that if all species of
animals have proceeded from some common stock, the general character of
their structural relations, and of our systems of classification, which
express those relations, would be just what we find them to be. In
other words, the hypothetical cause is, so far, competent to produce
effects similar to those of the real cause.