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.