han
many generally acknowledged races of our domestic animals; these three
species if domesticated would almost certainly vary, and races adapted
to different ends might be selected out of such variations. In this
state they would probably breed together, and their offspring would
possibly be quite, and probably in some degree, fertile; and in either
case, by continued crossing, one of these specific forms might be
absorbed and lost in another. I repeat, shall we then say that a pair,
or a gravid female, of each of these three species of rhinoceros, were
separately created with deceptive appearances of true relationship, with
the stamp of inutility on some parts, and of conversion in other parts,
out of the inorganic elements of Java, Sumatra and Malacca? or have they
descended, like our domestic races, from the same parent-stock? For my
own part I could no more admit the former proposition than I could admit
that the planets move in their courses, and that a stone falls to the
ground, not through the intervention of the secondary and appointed law
of gravity, but from the direct volition of the Creator.

{516} The discussion on the three species of _Rhinoceros_ which
also occurs in the Essay of 1842, p. 48, was omitted in Ch. XIV of
the _Origin_, Ed. i.

Before concluding it will be well to show, although this has
incidentally appeared, how far the theory of common descent can
legitimately be extended{517}. If we once admit that two true species of
the same genus can have descended from the same parent, it will not be
possible to deny that two species of two genera may also have descended
from a common stock. For in some families the genera approach almost as
closely as species of the same genus; and in some orders, for instance
in the monocotyledonous plants, the families run closely into each
other. We do not hesitate to assign a common origin to dogs or cabbages,
because they are divided into groups analogous to the groups in nature.
Many naturalists indeed admit that all groups are artificial; and that
they depend entirely on the extinction of intermediate species. Some
naturalists, however, affirm that though driven from considering
sterility as the characteristic of species, that an entire incapacity to
propagate together is the best evidence of the existence of natural
genera. Even if we put on one side the undoubted fact that some species
of the same genus will not breed together, we cannot poss