But
it is expressly stated that they are not constant; they appear
"frequently," or "occasionally," they are "not strictly inherited, for
they occur or fail in animals of the same litter;" and they are not
always symmetrical, sometimes appearing on one side of the face alone.
Now whatever may be the cause or explanation of these anomalous
appendages they cannot be classed with "specific characters," the most
essential features of which are, that they _are_ symmetrical, that they
_are_ inherited, and that they _are_ constant. Admitting that this
peculiar appendage is (as Mr. Romanes says rather confidently, "we
happen to know it to be") wholly useless and meaningless, the fact would
be rather an argument against specific characters being also
meaningless, because the latter never have the characteristics which
this particular variation possesses.
These useless or non-adaptive characters are, apparently, of the same
nature as the "sports" that arise in our domestic productions, but
which, as Mr. Darwin says, without the aid of selection would soon
disappear; while some of them may be correlations with other characters
which are or have been useful.
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