Page:George Archdall Reid 1896 The present evolution of man.djvu/117

Rh "But while I cannot admit my failure to understand Weismann, I confess that I do not understand Dr. Romanes. How when natural selection, direct or reversed, is set aside, the mere cessation of selection should cause decrease of an organ irrespective of the direct effects of disuse, I am unable to see. Clearer conceptions of this matter would be reached if, instead of thinking in abstract terms, the physiological processes concerned were brought into the foreground. Beyond the production of changes in the sizes of parts by the selection of fortuitously-arising variations, I can see but one other cause for the production of them—the competition among the parts for nutriment. This has the effect that active parts are well supplied and grow, while inactive parts are ill supplied and dwindle. This competition is the cause of 'economy of growth'; this is the cause of decrease from disuse; and this is the only conceivable cause of that decrease which Dr. Romanes contends follows the cessation of selection. The three things are aspects of the same thing. And now, before leaving this question, let me remark on the strange proposition which has to be defended by those who deny the dwindling of organs by disuse. Their proposition amounts to this—that for a hundred generations an inactive organ may be partially denuded of blood all through life, and yet in the hundredth generation will be produced of just the same size as in the first" (pp. 67–8).

I have already set forth my reasons for believing that, as regards any structure, retrogression follows Cessation of Selection, because there is a greater tendency in every organism to vary ancestor-wards than in any other direction, and that therefore retrogression in such a case is nothing other than a continued lapsing of inborn variations, the more recent in the phylogeny first, the more ancient in succession later, till there is at length a reversion to the remotest condition, the condition when there was no such structure. But as