ENVIRONMENT AND EVOLUTION KROPOTKIN. 417 



formerly used to be quoted as proofs of the inheritance of acquired 

 characters, he certainly induced biologists to go deeper into the 

 subject of heredity. But that was all. In his attempts at construc- 

 tive work he failed. He had not that power of inductive generaliza- 

 tion which leads modern science to its great discoveries. His 

 hypotheses were brilliantly and imaginatively developed suggestions, 

 but they were not brilliant inductive generalizations. They even 

 lacked originality. 



IV. 



However, it may be asked : Why do we not know more cases where 

 the hereditary transmission of acquired characters has been proved 

 by experiment? Why have we not yet proofs of acquired characters 

 being retained for a number of generations, even though the offspring 

 was taken back to its old environment? These two questions cer- 

 tainly deserve a careful examination. 



The reasons are many. To begin w r ith, it is extremely difficult to 

 breed plants, and still more so higher animals, in surroundings suf- 

 ficiently different from the normal ones for altering the distinctive 

 characters of a species. Especially is it difficult to make animals 

 reproduce themselves in such conditions. In the best conducted 

 experiments it happened over and over again that the second genera- 

 tion, when it was bred in an unusual environment, perished entirely ; 

 in the best cases only one or two individuals survived. 



Besides, it was only gradually learned by the experimenters 

 that, in order to obtain an inheritable variation, the modifying 

 cause m;ust act at a certain period of the individual's life, when 

 its reproductive cells are specially sensitive to new impressions. 1 

 And then the experiments require time. While it is very difficult 

 to breed several generations in succession in unusual conditions, 

 it is precisely several, or even many generations which must 

 be under the influence of a modifying cause in order to produce 

 a more or less stable variation. Lamarck, in stating his two 

 laws of variation, was careful to indicate that the changes must be 

 slow, and that they must take place for a succession of generations, in 

 order to be inherited and maintained later on for some time. Darwin 

 repeatedly insisted upon this. But only now the conditions under 

 which such experiments must be conducted are beginning to be 

 realized in special climatic stations and laboratories. Up till quite 

 lately such experiments were not in favor in most of the west 

 European universities. 



Finally, during the first decades after the appearance of the 

 Origin of Species, research was chiefly directed, as we have seen, 



1 Darwin knew it and mentioned it in several places in Variation ; but when the fact 

 was established by the experiments of Merrifield, Standfuss, and so on, it was received 

 as a new discovery. 



