"There can be no doubt, from the facts given in the early part of this chapter, that extremely slight changes in the conditions of life sometimes act in a definite manner on our already variable domesticated productions [productions, therefore, with regard to which uniformity and 'stability' of modification are least likely to arise]; and, as the action Of changed conditions in causing general or indefinite variability is accumulative, so it may be with their definite action. Hence it is possible that _great_ and _definite_ modifications of structure may result from altered conditions acting during a long series of generations. In some few instances a marked effect has been produced quickly on _all_, or _nearly all_, the individuals which have been exposed to some considerable change of climate, food, or other circumstance[172]." [172] _Variation_, &c., vol. ii. p. 280. Once more, in order to show that he retained these views to the end of his life, I may quote a passage from the second edition of the _Descent of Man_, which is the latest expression of his opinion upon these points:-- "Each of the endless diversities in plumage, which we see in our domesticated birds, is, of course, the result of some definite cause; and under natural and more uniform conditions, some one tint, _assuming that it was in no way injurious, would almost certainly sooner or later prevail_. The free-intercrossing of the many individuals belonging to the same species would ultimately tend to make any change of colour thus induced _uniform in character_.... Can we believe that the very slight differences in tints and markings between, for instance, the female black-grouse and red-grouse serve as a protection? Are partridges as they are now coloured, better protected than if they had resembled quails? Do the slight differences between the females of the common pheasant, the Japan and golden pheasants, serve as a protection, or might not their plumage have been interchanged with impunity? From what Mr. Wallace has observed of the habits of certain gallinaceous birds in the East, he thinks that such slight differences are beneficial. For myself, I will only say, I am not convinced[173]." [173] _Descent of Man_, pp. 473-4. Yet "convinced" he certainly must have been on merely _a priori_ grounds, had he countenanced Mr. Wallace's reasoning from the general theory of natural selection; and the fact that he here fails to be convinced even by "what Mr. Wallace has observed of the habits of certain gallinaceous birds," appears to indicate that he had considered the question of utility with special reference to Mr. Wallace's opinion. That opinion was then, as now, the avowed result of a theoretical prepossession; and this prepossession, as the above quotations sufficiently show, was expressly repudiated by Darwin.