t merely explains, but necessitates
what exists. Granted the law, and many of the most important facts in
Nature could not have been otherwise, but are almost as necessary
deductions from it, as are the elliptic orbits of the planets from the
law of gravitation.

II.

ON THE TENDENCY OF VARIETIES TO DEPART INDEFINITELY FROM THE ORIGINAL
TYPE.[D]

+--------------------------------------------------------------+
| [D] Written at Ternate, February, 1858; and published in the |
| Journal of the Proceedings of the Linnaean Society for |
| August, 1858. |
+--------------------------------------------------------------+

_Instability of Varieties supposed to prove the permanent distinctness
of Species._

One of the strongest arguments which have been adduced to prove the
original and permanent distinctness of species is, that _varieties_
produced in a state of domesticity are more or less unstable, and often
have a tendency, if left to themselves, to return to the normal form of
the parent species; and this instability is considered to be a
distinctive peculiarity of all varieties, even of those occurring among
wild animals in a state of nature, and to constitute a provision for
preserving unchanged the originally created distinct species.

In the absence or scarcity of facts and observations as to _varieties_
occurring among wild animals, this argument has had great weight with
naturalists, and has led to a very general and somewhat prejudiced
belief in the stability of species. Equally general, however, is the
belief in what are called "permanent or true varieties,"--races of
animals which continually propagate their like, but which differ so
slightly (although constantly) from some other race, that the one is
considered to be a _variety_ of the other. Which is the _variety_ and
which the original _species_, there is generally no means of
determining, except in those rare cases in which the one race has been
known to produce an offspring unlike itself and resembling the other.
This, however, would seem quite incompatible with the "permanent
invariability of species," but the difficulty is overcome by assuming
that such varieties have strict limits, and can never again vary further
from the original type, although they may return to it, which, from the
analogy of the domesticated animals, is considered to be highly
probable, if not certainly prove