I have already shown that every part of
the organism, in common species, does vary to a very considerable
amount, in a large number of individuals, and in the same locality; the
only point that remains to be discussed is, whether any or most of these
variations are "beneficial." But every one of these variations consists
either in increase or diminution of size or power of the organ or
faculty that varies; they can all be divided into a more effective and a
less effective group--that is, into one that is more beneficial or less
beneficial. If less size of body would be beneficial, then, as half the
variations in size are above and half below the mean or existing
standard of the species, there would be ample beneficial variations; if
a darker colour or a longer beak or wing were required, there are always
a considerable number of individuals darker and lighter in colour than
the average, with longer or with shorter beaks and wings, and thus the
beneficial variation must always be present. And so with every other
part, organ, function, or habit; because, as variation, so far as we
know, is and always must be in the two directions of excess and defect
in relation to the mean amount, whichever kind of variation is wanted is
always present in some degree, and thus the difficulty as to
"beneficial" variations occurring, as if they were a special and rare
class, falls to the ground.
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