GERMINAL SELECTION 115 



produce as good offspring as those with better eyes, and the conse- 

 quence of this must be that there will be a general deterioration of 

 eyes, because the bad ones can be transmitted as well as the good, 

 and thus the selection of good eyes is made impossible. 



The mixture thus arising may be compared to a fine wine to 

 which a litre of vinegar has been added; the whole cask is ruined 

 because the vinegar mingles with every drop of the wine. As 

 deviations from the normal are always occurring in every part of 

 every species, and among them some that lessen the value of the 

 organ, rarely perhaps at first, but after a time in every generation, 

 a sinking of the organ from the highest point of possible perfection 

 becomes inevitable as soon as the organ becomes superfluous. The 

 functional uselessness of the organ must go on increasing the longer 

 it is disused, as will readily be admitted if it be remembered that 

 only the most perfect adaptation of all the separate parts of an organ 

 can maintain its functional capacity, that all the parts of an organ 

 are subject to variation, and that every deviation from the optimum 

 implies a further deterioration of the whole. An eye, for instance, 

 can no longer vary in the direction of 'better' if it has already 

 reached the highest possible point of perfection; every further 

 variation must deteriorate it. 



Romanes gave expression to this idea, that the cessation of 

 natural selection alone must cause the degeneration of a part, a decade 

 before I did, but neither he nor the scientific world of his time 

 attached great importance to it, and it Avas forgotten again. This 

 was intelligible enough, for, at that time, the validity of the 

 Lamarckian principle had not been called in question, and therefore the 

 need for some other principle to explain the disappearance of disused 

 parts had not begun to be felt. 



I found myself in quite a different position. As my douV)ts 

 regarding the Lamarckian principle grew greater and greater, I was 

 oblio-ed to seek for some other factor in modification, which should be 

 sufficient to effect the degeneration of a disused part, and for a tnne 

 I thought I had found this in panmixia, that is, in the mingling of 

 all together, well and less well equipped alike. This factor does 

 certainly operate, but the more I thought over it the clearer it 

 became to me that there must be some other factor at work as well, 

 for while panmixia might explain the deterioration of an organ, it 

 could not explain its decrease in size, its gradual wearing away, and 

 ultimate total disappearance. Yet this is the path followed, slowly 

 indeed, but quite surely, by all organs which have become useless. 

 If panmixia alone guided the deterioration of the organ, and it was 



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