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 in circumstances
than the other, will inevitably, in the long run, eliminate it.

A frequent and a just objection to the Lamarckian hypothesis of the
transmutation of species is based upon the absence of transitional
forms between many species. But against the Darwinian hypothesis this