68 EVOLUTION AND ANIMAL LIFE 



ratio — that is, by addition ; therefore, whatever may be the ratio 

 of increase, a geometrical progression will sooner or later outrun 

 an arithmetical one. Hence sooner or later the world must be 

 overstocked, did not vice, misery, or prudence come in as checks, 

 reducing the ratio of multiplication. This law has been criti- 

 cised as a partial truth, so far as man is concerned. This means 

 simply that there are factors also in evolution other than those 

 recognized by Malthus. Nevertheless, Malthus's law is a sound 

 statement of one great factor. And this law is simply the ex- 

 pression of the struggle for existence as it appears among men. 



The doctrine of organic evolution was first placed on a firm 

 basis by Darwin, because Darwin was the first who clearly 

 defined the force of natural selection. Darwin, however, rec- 

 ognized other factors, known or hypothetical, and was inter- 

 ested more in shovving the fact of descent and one cause of 

 modification than in insisting on the all-sufFiciency of the cause 

 especially defined by himself. 



In later times, Weismann and his followers have laid more 

 exclusive stress on natural selection and its Allmacht or ex- 

 clusive power in bringing about organic evolution. This view 

 is known as Neo-Darwinism and the school of workers who 

 profess it as Neo-Darwinians. Few investigators question 

 the far-reaching influence of natural selection, but there are 

 many phases in organic evolution which cannot be ascribed 

 to it. Hence the search for other factors has been assiduously 

 prosecuted, and doubts of Darwinism have been widely ex- 

 pressed; but this doubting has been thrown not so much on 

 the Darwinism of Darwin, nor, as a rule, on the law of natural 

 selection, but rather on the Allmacht claimed for it by Weis- 

 mann and his associates. 



Without attempting any elaborate discussion of questions 

 still far from settled we may venture these suggestions : 



1. Given the facts of individual variation, of inheritance, 

 and some check to freedom of migration, natural selection would 

 accomplish some form of organic evolution; species would be 

 formed by the survival of the adapted, adaptations would be 

 perpetuated, and minor differences would develop in time into 

 deep-seated differences. 



2. With natural selection alone, however, the actual facts in 

 organic evolution as we know them would apparently not be 

 achieved. 



