ith great rapidity. The brow-antlers
protect the face and eyes, while the widely spreading horns prevent
injury to the neck or flanks. Thus an organ which was certainly
developed as a sexual weapon, has been so guided and modified during its
increase in size as to be of use in other ways. A similar use of the
antlers of deer has been observed in India.[44]

The various classes of facts now referred to serve to show us that, in
the case of the two higher groups--mammalia and birds--almost all the
characters by which species are distinguished from each other are, or
may be, adaptive. It is these two classes of animals which have been
most studied and whose life-histories are supposed to be most fully
known, yet even here the assertion of inutility, by an eminent
naturalist, in the case of two important organs, has been sufficiently
met by minute details either in the anatomy or in the habits of the
groups referred to. Such a fact as this, together with the extensive
series of characters already enumerated which have been of late years
transferred from the "useless" to the "useful" class, should convince
us, that the assertion of "inutility" in the case of any organ or
peculiarity which is not a rudiment or a correlation, is not, and can
never be, the statement of a fact, but merely an expression of our
ignorance of its purpose or origin.[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 bree