78 DARWINISM TO-DAY. 



this is not the case the average of the survivors cannot 

 change. Weismann himself has in recent years recognised 

 the inadequacy of panmixia alone to explain degenerative 

 phenomena. He says: 12 . . . "In most retrogressive pro- 

 cesses active selection in Darwin's sense plays no part, 

 and advocates of the Lamarckian principle, as above re- 

 marked, have rightly denied that active selection, that is, 

 the selection of individuals possessing the useless organ in 

 its most reduced state, is sufficient to explain the process of 

 degeneration. I, for my part, have never assumed this, 

 and have on this very account enunciated the principle of 

 panmixia. Now, although this, as I have still no reason 

 for doubting, is a perfectly correct principle, which really 

 does have an essential and indispensable share in the process 

 of retrogression, still it is not alone sufficient for a full ex- 

 planation of the phenomena. My opponents, in advancing 

 this objection, were right, to the extent indicated, and as 

 I expressly acknowledge, although they were unable to 

 substitute anything positive in its stead or to render my 

 explanation complete. The very fact of the cessation of 

 control over the organ is sufficient to explain its degenera- 

 tion, that is, its deterioration, the disharmony of its parts, 

 but not the fact which actually and always occurs where an 

 organ has become useless viz., its gradual and unceasing 

 diminution continuing for thousands and thousands of years 

 and culminating in its final and absolute effacement." 



To supply the lack in the present neo-Darwinian explana- 

 tion of retrogression Weismann calls on his new theory of 

 germinal selection, the "rehabilitates of the natural selec- 

 tion theory" (for an account of this theory see chapter viii). 

 But Wolff and Morgan and others have shown how unsatis- 

 factory and inadequate this third attempt at an explanation 

 is, even if we grant the actuality of germinal selection, a 

 hypothesis which has by no means met with any general 

 acceptance by biologists. 



