"I have made these remarks only to show that, if we are unable to account for the characteristic differences of our several domestic breeds, which nevertheless are generally admitted to have arisen through ordinary generation from one or a few parent stocks, we ought not to lay too much stress on our ignorance of the precise cause [i.e. whether natural selection or some other cause] of the slight analogous differences between true _species_.... I fully admit that _many_ structures are now of no use to their possessors, and may never have been of any use to their progenitors; but this does not prove that they were formed solely for beauty or variety. No doubt the definite action of changed conditions, and the various causes of modification, lately specified, have all produced an effect, _probably a great effect, independently of any advantage thus gained_.... It is scarcely possible to decide how much allowance ought to be made for such causes of change, as the definite action of external conditions, so-called spontaneous variations, and the complex laws of growth; but, _with these important exceptions_, we may conclude that the structure of every living creature either now is, or formerly was, of some direct or indirect use to its possessor[161]." [161] _Descent of Man_, pp. 159-60. Here again, if we remember how "important" these "exceptions" are, I cannot understand any one doubting Darwin's opinion to have been that a large proportional number of specific characters are useless. For that it is "species" which he here has mainly in his mind is evident from what he says when again alluding to the subject in his "Summary of the Chapter"--namely, "In _many_ other cases [i.e. in cases where natural selection has not been concerned] modifications are probably the direct result of the laws of variation or of growth, independently of any good having been thus gained." Now, not only do these "laws" apply as much to species as they do to genera; "but," the passage goes on to say, "even such structures have often, we may feel assured, been subsequently taken advantage of, and still further modified, for the good of _species_ under new conditions of life." Obviously, therefore, the inutility in such cases is taken to have been prior to any utility subsequently acquired; and genera are not historically prior to the species in which they originate. Here is another quotation:--