Alfred Russel Wallace 



the weakest and most inconclusive thing he has yet written. 

 At p. 17 he states his theory as to degeneration of eyes, 

 and again, on p. 18, of anthers and filaments; but in both 

 cases he fails to prove it, and apparently does not see 

 that his panmixia, or '' cessation of selection," cannot pos- 

 sibly produce continuous degeneration culminating in the 

 total or almost total disappearance of an organ. Komanes 

 and others have pointed out this weakness in his theory, 

 but he does not notice it, and goes on calmly throughout 

 the essay to assume that mere panmixia must cause pro- 

 gressive degeneration to an unlimited extent; whereas all 

 it can do is to effect a reduction to the average of the total 

 population on which selection has been previously worked. 

 He says '^ individuals with weak eyes would not be elimi- 

 nated," but omits to notice that individuals with strong 

 eyes would also " not be eliminated," and as there is no 

 reason alleged why variations in all directions should not 

 occur as before, the free intercrossing would tend to keep 

 up a mean condition only a little below that which was 

 kept up by selection. It is clear that some form of selec- 

 tion must always co-operate in degeneration, such as 

 economy of growth, which he hardly notices except as a 

 possible but not a necessary factor, or actual injurious- 

 ness. It appears to me that what is wanted is to take a 

 number of typical cases, and in eaeh of them show how 

 Natural Selection comes in to carry on the degeneration 

 begun by panmixia. Weismann's treatment of the subject 

 is merely begging the question. — Yours faithfully, 



A. R. W.iLLACE. 



To Prof. Poulton 



ParkstoTie, Dorset. August 29, 1892. 



My dear Mr. Poulton, — As to panmixia you have quite 

 misunderstood my position. By the '' mean condition," I 



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