306 Darwin, and after Darwin. 



question of amount, there is no doubt on any side that 

 panmixia alone causes degeneration more rapidly where it 

 has to do with complexity of organization, than it does where 

 it is concerned with a mere reduction of mass. 



The question as to the amount of degeneration that is 

 caused by the cessation of selection alone is without any 

 practical importance where species in a state of nature are 

 concerned, because here the cessation of selection is probably 

 always associated more or less with the reversal of it ; and it 

 is as impossible as it is immaterial to determine the relative 

 shares which these two co-operating principles take in 

 bringing about the observed results. But where organisms 

 in a state of domestication are concerned, the importance of 

 the question before us is very great. For if the cessation of 

 selection alone is capable of reducing an organ through 

 10 or 12 per cent, of its original size, nearly all the direct 

 evidence on which Darwin relied in favour of use-inheritance 

 is destroyed. On the other hand, if reduction through 5 per 

 cent, be deemed a " very liberal estimate " of what this 

 principle can accomplish, the whole body of Darwin's direct 

 evidence remains as he left it. I have now given my reasons 

 for rejecting this lower estimate on the one hand, and what 

 seems to me the extravagant estimate of Weismann on the 

 other. But my own intermediate estimate is enough to 

 destroy the apparent proof of use-inheritance that was given 

 by Darwin. Therefore it remains for those who deny 

 Lamarckian principles, either to accept some such estimate, 

 or else to acknowledge the incompatibility of any lower one 

 with the opinion that there is no evidence in favour of these 

 principles. 



