artificial breeds or races of animals and plants, have been produced by
one method. The breeder--and a skilful one must be a person of much
sagacity and natural or acquired perceptive faculty--notes some slight
difference, arising he knows not how, in some individuals of his stock.
If he wish to perpetuate the difference, to form a breed with the
peculiarity in question strongly marked, he selects such male and
female individuals as exhibit the desired character, and breeds from
them. Their offspring are then carefully examined, and those which
exhibit the peculiarity the most distinctly are selected for breeding,
and this operation is repeated until the desired amount of divergence
from the primitive stock is reached. It is then found that by
continuing the process of selection--always breeding, that is, from
well-marked forms, and allowing no impure crosses to interfere,--a race
may be formed, the tendency of which to reproduce itself is exceedingly
strong; nor is the limit to the amount of divergence which may be thus
produced known, but one thing is certain, that, if certain breeds of
dogs, or of pigeons, or of horses, were known only in a fossil state,
no naturalist would hesitate in regarding them as distinct species.

But, in all these cases we have 'human interference'. Without the
breeder there would be no selection, and without the selection no
race. Before admitting the possibility of natural species having
originated in any similar way, it must be proved that there is in nature
some power which takes the place of man, and performs a selection 'sua
sponte'. It is the claim of Mr. Darwin that he professes to have
discovered the existence and the 'modus operandi' of this natural
selection, as he terms it; and, if he be right, the process is perfectly
simple and comprehensible, and irresistibly deducible from very
familiar but well nigh forgotten facts.