98 THE THEORY OF MUTATIONS 



new, and evolution, of course, is not restricted 

 to the increase of the already existing peculiarities, 

 but depends chiefly on the continuous addition 

 of new characters to the stock. Fluctuations always 

 oscillate around an average, and, if removed 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 are 

 not linked to them by intermediates." Again, it 

 must be insisted how important this question of 

 fluctuations is to present-day ideas of evolution, 

 since the theory of the accumulation of small 

 changes underlies the ideas of both the two chief 

 opposing camps of biologists, the Neo-Lamarck- 

 ians, who assume a modifying agency on the part 

 of the environment, and the Neo-Darwinians who 

 refuse to accept this view. De Vries, Bateson and 

 those who agree with them are consequently in 

 opposition to both these groups, and deny a doc- 

 trine fundamental to both their creeds. De Vries 

 argues that the variations on which both these 

 schools of thought have relied are wholly different 

 from what he calls mutations, and believes to be 

 alone capable of producing new elementary 

 species. Mutations are characterized, according 

 to his view, by the " production of something 

 new, by the acquirement of a character hitherto 

 unnoticed in the line of their ancestors. On the 

 contrary, varieties, in most cases, evidently owe 

 their origin to the loss of an already existing 



