ral. Groups having the
morphological character of species, distinct and permanent races
in fact, have been so produced over and over again; but there is
no positive evidence, at present, that any group of animals has, by
variation and selective breeding, given rise to another group which
was, even in the least degree, infertile with the first. Mr. Darwin is
perfectly aware of this weak point, and brings forward a multitude
of ingenious and important arguments to diminish the force of the
objection. We admit the value of these arguments to their fullest
extent; nay, we will go so far as to express our belief that
experiments, conducted by a skilful physiologist, would very probably
obtain the desired production of mutually more or less infertile breeds
from a common stock, in a comparatively few years; but still, as the
case stands at present, this "little rift within the lute" is not to be
disguised nor overlooked.

In the remainder of Mr. Darwin's argument our own private ingenuity
has not hitherto enabled us to pick holes of any great importance; and
judging by what we hear and read, other adventurers in the same field
do not seem to have been much more fortunate. It has been urged, for
instance, that in his chapters on the struggle for existence and on
natural selection, Mr. Darwin does not so much prove that natural
selection does occur, as that it must occur; but, in fact, no other sort
of demonstration is attainable. A race does not attract our attention
in Nature until it has, in all probability, existed for a considerable
time, and then it is too late to inquire into the conditions of its
origin. Again, it is said that there is no real analogy between the
selection which takes place under domestication, by human influence,
and any operation which can be effected by Nature, for man interferes
intelligently. Reduced to its elements, this argument implies that an
effect produced with trouble by an intelligent agent must, a fortiori,
be more troublesome, if not impossible, to an unintelligent agent. Even
putting aside the question whether Nature, acting as she does according
to definite and invariable laws, can be rightly called an unintelligent
agent, such a position as this is wholly untenable. Mix salt and sand,
and it shall puzzle the wisest of men, with his mere natural appliances,
to separate all the grains of sand from all the grains of salt; but a
shower of rain will effect the same object in ten minutes. An