note: The first step
only towards experimental demonstration has been taken. Experiments
now begun might, a couple of centuries hence, furnish data of
incalculable value, which ought to be supplied to the science of the
future.] He made himself acquainted with what could, without any
manner of doubt, be done in the way of producing variation. He
associated himself with pigeon-fanciers--bought, begged, kept, and
observed every breed that he could obtain. Though derived from a
common stock, the diversities of these pigeons were such that 'a score
of them might be chosen which, if shown to an ornithologist, and he
were told that they were wild birds, would certainly be ranked by him
as well-defined species.' The simple principle which guides the
pigeon-fancier, as it does the cattle-breeder, is the selection of
some variety that strikes his fancy, and the propagation of this
variety by inheritance. With his eye still directed to the particular
appearance which he wishes to exaggerate, he selects it as it
reappears in successive broods, and thus adds increment to increment
until an astonishing amount of divergence from the parent type is
effected. The breeder in this case does not produce the elements of
the variation. He simply observes them, and by selection adds them
together until the required result has been obtained. 'No man,' says
Mr. Darwin, 'would ever try to make a fantail till he saw a pigeon
with a tail developed in some slight degree in an unusual manner, or a
pouter until he saw a pigeon with a crop of unusual size.' Thus nature
gives the hint, man acts upon it, and by the law of inheritance
exaggerates the deviation.

Having thus satisfied himself by indubitable facts that the
organisation of an animal or of a plant (for precisely the same
treatment applies to plants). is to some extent plastic, he passes
from variation under domestication to variation under nature. Hitherto
we have dealt with the adding together of small changes by the
conscious selection of man. Can Nature thus select? Mr. Darwin's
answer is, 'Assuredly she can.' The number of living things produced
is far in excess of the number that can be supported; hence at some
period or other of their lives there must be a struggle for existence.
And what is the infallible result? If one organism were a perfect
copy of the other in regard to strength, skill, and agility, external
conditions would decide. But this is not the case. Here we