Wallace s Selection Theory. 39 



fluctuating variability as a phenomenon of an entirely 

 different kind.^ 



To sum up, we see that Darwin always distinguished 

 between individual differences and single variations and 

 that he ascribed to the latter at least a very considerable 

 role in the origin of species. It was only by the pressure 

 of criticism that he finally gave up this view and gave 

 the place of honor to the ever present individual varia- 

 tions. 



§ 3- WALLACE'S SELECTION THEORY. 



In his book on ''Darwinism" Alfred Russel Wal- 

 lace has collected in an excellent and convincing manner 

 a valuable mass of evidence for the theory of descent.^ 

 Few authors except Darwin have taken such a prom- 

 inent part in fighting for this theory, as he. His book 

 ''Darwinism" consists essentially of two parts. In the 

 first sections Wallace deals with variability and selec- 

 tion, in the second he describes the wonderful adapta- 

 tions of animals and plants to their environment and 

 seeks to explain them on the basis of Darwin's theory 

 by bringing out as forcibly as possible the agreement 

 between the demands of the theory and the facts them- 

 selves. This latter half is undoubtedly the most interest- 

 ing of the whole work. But I shall only discuss his 

 theory of selection in this book. 



Wallace's selection theory differs from that of 

 Darwin in one essential point. Wallace regards the 

 ever present individual variation as the material from 

 which natural selection forms new species. It is his main 



^ See also my Intraccllularc Pangenesis, pp. 73-74, 210, etc. 



^ A. R. Wallace, Darzvinism, an Exposition of the Theory of 

 Natural Selection zvith Some of its Applications. London, 1889, 

 2d. ed. 



