nian theory is the variability of species,
and it is quite useless to attempt even to understand that theory, much
less to appreciate the completeness of the proof of it, unless we first
obtain a clear conception of the nature and extent of this variability.
The most frequent and the most misleading of the objections to the
efficacy of natural selection arise from ignorance of this subject, an
ignorance shared by many naturalists, for it is only since Mr. Darwin
has taught us their importance that varieties have been systematically
collected and recorded; and even now very few collectors or students
bestow upon them the attention they deserve. By the older naturalists,
indeed, varieties--especially if numerous, small, and of frequent
occurrence--were looked upon as an unmitigated nuisance, because they
rendered it almost impossible to give precise definitions of species,
then considered the chief end of systematic natural history. Hence it
was the custom to describe what was supposed to be the "typical form" of
species, and most collectors were satisfied if they possessed this
typical form in their cabinets. Now, however, a collection is valued in
proportion as it contains illustrative specimens of all the varieties
that occur in each species, and in some cases these have been carefully
described, so that we possess a considerable mass of information on the
subject. Utilising this information we will now endeavour to give some
idea of the nature and extent of variation in the species of animals and
plants.

It is very commonly objected that the widespread and constant
variability which is admitted to be a characteristic of domesticated
animals and cultivated plants is largely due to the unnatural conditions
of their existence, and that we have no proof of any corresponding
amount of variation occurring in a state of nature. Wild animals and
plants, it is said, are usually stable, and when variations occur these
are alleged to be small in amount and to affect superficial characters
only; or if larger and more important, to occur so rarely as not to
afford any aid in the supposed formation of new species.

This objection, as will be shown, is utterly unfounded; but as it is one
which goes to the very root of the problem, it is necessary to enter at
some length into the various proofs of variation in a state of nature.
This is the more necessary because the materials collected by Mr. Darwin
bearing on this question have n