On the view of each organism with all
its separate parts having been specially created, how utterly inexplicable
is it that organs bearing the plain stamp of inutility, such as the teeth
in the embryonic calf or the shrivelled wings under the soldered
wing-covers of many beetles, should so frequently occur. Nature may be
said to have taken pains to reveal her scheme of modification, by means of
rudimentary organs, of embryological and homologous structures, but we are
too blind to understand her meaning.
I have now recapitulated the facts and considerations which have thoroughly
convinced me that species have been modified, during a long course of
descent. This has been effected chiefly through the natural selection of
numerous successive, slight, favourable variations; aided in an important
manner by the inherited effects of the use and disuse of parts; and in an
unimportant manner, that is, in relation to adaptive structures, whether
past or present, by the direct action of external conditions, and by
variations which seem to us in our ignorance to arise spontaneously. It
appears that I formerly underrated the frequency and value of these latter
forms of variation, as leading to permanent modifications of structure
independently of natural selection. But as my conclusions have lately been
much misrepresented, and it has been stated that I attribute the
modification of species exclusively to natural selection, I may be
permitted to remark that in the first edition of this work, and
subsequently, I placed in a most conspicuous position--namely, at the close
of the Introduction--the following words: "I am convinced that natural
selection has been the main but not the exclusive means of modification.
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