608 Validity of the Doctrine of Mutation. 



consists merely in an oscillation around a given point of 

 equilibrium ; whilst the formation of new species necessi- 

 tates the attainment of a new equilibrium. Especially in 

 America has this view made great progress, as has been 

 described by Conn in an admirable exposition in his new 

 work on evolution.-^ 



Of the numerous writings which we owe to Wal- 

 lace's school, I shall only mention here that on Natural 

 Selection and Tropical Nature, of this author (1895), 

 and Plate's critical exposition of Wallace's theory.- 

 Although Plate, at the conclusion of his clear and per- 

 ceptive critique of the questions which pertain to this 

 point, declares in favor of the theory of selection, his 

 work, of all those of which I have made use, gives me the 

 impression of the greatest objectivity; and I am con- 

 vinced that the gulf between his views and those I hold 

 will surely be bridged over some day. Therefore I refer 

 the reader to his book for a closer study of these ques- 

 tions, and shall confine myself here to a few points which 

 stand in the closest relation to those discussed above. 



1. The significance of fluctuating variability is very 

 limited, whereas the explanation of adaptations demands 

 almost unlimited variability. In earlier days when the 

 law of Quetelet was only known to apply to anthro- 

 pology, almost all the changes of plants and animals 

 were considered to be the consequences of ordinary varia- 

 bility, but now this is shown lO be governed by laws which 

 largely curtail its importance. In the first part of the 

 first volume this theme has been discussed in detail, and 

 I may here simply refer the reader to those chapters. 



^ H. W. Conn, The Method of Evolution, New York, 1900, p. 132. 



^L. Plate, Ucher Bcdcutung and Tragzvcitc des Darivin'schcn 

 Selectionsprincips, Leipsic, 1900. A very complete bibliographical 

 list will be found on pp. 145-153 of this book. 



