[45]
_Instability of Non-adaptive Characters._
One very weighty objection to the theory that _specific_ characters can
ever be wholly useless (or wholly unconnected with useful organs by
correlation of growth) appears to have been overlooked by those who have
maintained the frequency of such characters, and that is, their almost
necessary instability. Darwin has remarked on the extreme variability of
secondary sexual characters--such as the horns, crests, plumes, etc.,
which are found in males only,--the reason being, that, although of some
use, they are not of such direct and vital importance as those adaptive
characters on which the wellbeing and very existence of the animals
depend. But in the case of wholly useless structures, which are not
rudiments of once useful organs, we cannot see what there is to ensure
any amount of constancy or stability. One of the cases on which Mr.
Romanes lays great stress in his paper on "Physiological Selection"
(_Journ. Linn. Soc._, vol. xix. p. 384) is that of the fleshy appendages
on the corners of the jaw of Normandy pigs and of some other breeds.
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