192 DARWINISM TO-DAY. 



panmixia an explanation not involving the admission of 

 any new organ-modifying factor, have been able to see how 

 panmixia can do more than simply reduce the organ to a 

 certain stage below the original state of greatest effective- 

 ness. By resorting to mathematics several writers have 

 determined the exact unfortunately for their convincing 

 character several degrees of reduction or degeneration that 

 will result from panmixia. The difficulty of explaining 

 degeneration (to the degree in which it is manifest in thou- 

 sands of known cases) on the basis of panmixia alone, is that 

 there is included no factor or influence that would sum up 

 or cumulate variations in a retrogressive direction any more 

 than in any other. The Darwinian variations of the use- 

 less organ would, by the law of error, simply keep the organ, 

 thus abandoned by selection, swinging about a mean but 

 little below the condition possessed by the organ at the time 

 of its abandonment. If the organ were large enough, or of 

 a character \vhereby it would entail a constant considerable 

 disadvantageous expense of food material to maintain it, 

 then selection might, on a basis of an advantageous economy 

 of living, tend to reduce it to a non-disadvantageous size or 

 character. But this disadvantage, although easily presumed 

 by carrying out the rigour of the struggle to a logical ex- 

 treme, cannot, in fact, and biologists on the whole admit 

 this, in common sense be assumed. 



Lamarckism offers a perfectly simple and perfectly effect- 

 ive and satisfactory explanation of vestigial organs and the 

 modus of their degeneration. But to accept this 

 means to acce Pt the basic Principle of Lamarck- 



of vestigial j sm< namely, the inheritance of acquired char- 

 structures. . ,,, . , 



acters. And it is one of Weismann s most con- 



spicuous positive achievements that he has demonstrated the 

 unproved character of this theory. Lamarckism says that 

 the first fishes to go into the dark cave suffered a partial 

 individual degeneration of their eyes through disuse and 



