Now as these rare species do really vary
much less than the common species, and in many cases hardly vary at all,
it was very natural that a belief in the fixity of species should
prevail. It is not, however, as we shall see presently, the rare, but
the common and widespread species which become the parents of new forms,
and thus the non-variability of any number of rare or local species
offers no difficulty whatever in the way of the theory of evolution.
_Concluding Remarks._
We have now shown in some detail, at the risk of being tedious, that
individual variability is a general character of all common and
widespread species of animals or plants; and, further, that this
variability extends, so far as we know, to every part and organ, whether
external or internal, as well as to every mental faculty. Yet more
important is the fact that each part or organ varies to a considerable
extent independently of other parts. Again, we have shown, by abundant
evidence, that the variation that occurs is very large in
amount--usually reaching 10 or 20, and sometimes even 25 per cent of the
average size of the varying part; while not one or two only, but from 5
to 10 per cent of the specimens examined exhibit nearly as large an
amount of variation.
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