470 THE HISTORY OF BIOLOGY 



sea, have split up uniform groups of life-forms and created isolated areas of 

 development with accompanying new forms of genera and species. And 

 always variation and natural selection are sufficient to explain all phenom- 

 ena; since Aristotle produced his explanation of nature, no biologist has 

 ever conceived it his duty to the extent that Darwin did to explain anything 

 whatsoever. In this respect he takes the most extraordinary trouble to achieve 

 his purpose; in a letter to Lyell he expresses surprise that the bats of New 

 Zealand — of old the sole representatives of the mammals on the island — 

 had not made their home on the ground and developed into land-animals, 

 seeing that they had no competitors. And he ascribes to selection the most 

 remarkable powers; a traveller had seen a bear swimming in a North Ameri- 

 can river and snapping at insects in the water; Darwin thinks it not impos- 

 sible that, if food of this kind were abundant and there were no competitors, 

 a number of bears would become aquatic animals and would gradually 

 acquire larger and larger mouths, eventually becoming as monstrous as 

 whales. This strange conclusion, which is given in the first edition of the 

 work, but was modified in succeeding editions, gives striking evidence of 

 another weakness in Darwin's speculation: his lack of sense of a law-bound 

 necessity in existence. "I believe in no law of necessary development," he 

 expressly declares. The variations are certainly guided by laws, as mentioned 

 above, not, however, in any given direction, but in all possible directions, 

 and they are influenced, depending upon every chance, quite incalculably 

 by natural selection. But if, then, natural selection were guided by chance, 

 it would exclude the possibility of any law-bound phenomenon in existence. 

 Herein really lies the greatest weakness of the Darwinian doctrine of selec- 

 tion. It has, in fact, been sharply criticized — in modern times especially by 

 Oscar Hertwig in his work Das Werden der Organismen, the subject of which 

 is indicated by the subtitle: Eine Widerlegiing von Danvins Zujallstheorie. A 

 similar judgment was passed by Radl, who, moreover, points out that Dar- 

 win really applied the social conception of contemporary liberalism to life 

 in nature; which, as a matter of fact, is at once realized from the acknowl- 

 edged part played by Malthus's social doctrine in the working-out of Dar- 

 win's theory. This human-social conception of nature stands out clearly in 

 the above-mentioned statement regarding the bear, which, if the chance 

 offers, can take to swimming and develop into a whale. More applicable to 

 human-social life than to nature is also the form that his utterances often 

 take of fancies thrown out at random, which reminds one of a social re- 

 former's improvement schemes rather than of the binding conclusions of a 

 scientific investigator; "it would be easy," "it would offer no difficulty to 

 suppose," and other similar expressions frequently occur. This, of course, is 

 also due to his oft-recurring tendency to allow his thoughts to dally with all 

 kinds of possibilities — a tendency which, when combined with a belief in 



