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. And so,
while man may find it tax all his intelligence to separate any variety
which arises, and to breed selectively from it, the destructive agencies
incessantly at work in Nature, if they find one variety to be more soluble