18 Descent 



manifestly with specific and varietal characters. 

 By this method they may be proved to be in- 

 adequate ever to make a single step along the 

 great lines of evolution, in regard to progressive 

 as well as to retrograde development. 



First of all fluctuations are linear, amplify- 

 ing or lessening the existing qualities, but not 

 really changing their nature. They are not 

 observed to produce anything quite new, and 

 evolution of course, is not restricted to the in- 

 crease of the already existing peculiarities, but 

 depends chiefly on the continuous addition of 

 new characters to the stock. Fluctuations al- 

 ways oscillate around an average, and if re- 

 moved from this for some time, they show a 

 tendency to return to it. This tendency, called 

 retrogression, has never been observed to fail 

 as it should in order to free the new strain from 

 the links with the average, while new species 

 and new varieties are seen to be quite free from 

 their ancestors, and not linked to them by 

 intermediates. 



The last few lectures will be devoted to ques- 

 tions concerning the great problem of the anal- 

 ogy between natural and artificial selection. 

 As already stated, Darwin made this analogy 

 the foundation stone of his theory of descent, 

 and he met with the severest objections and crit- 

 icisms precisely on this point But I hope to 



