114 EVOLUTION AND ANIMAL LIFE 



seeming: reality vanislies with the death of the individual: 

 their young can perpetuate their specific pecuharities only if 

 the environmental conditions of their development are identical 

 with those wdiich attended the growing up of their parents. 

 Variations in this environment will determine variations in 

 them, and their father's kind will exist no more. 



The authors of this book beheve that more characters of 

 species than are commonly thought are of this shifty, ephemeral 

 character; that not a few so-cc^lled true species are only onto- 

 genetic species held for a num.ber of generations true to a type 

 simply because the environment, the extrinsic factors in the 

 development of all the individuals in these successive genera- 

 tions, are the same. But how these individual characteristics 

 and changes can be put into the heredity of the race we do not 

 understand. "There is no fixity in species other than that 

 due to the long-repeated ontogenetic reiteration of this or that 

 characteristic,'' says Luther Burbank. And he speaks from the 

 conviction forced on him through thirty years of the closest sort 

 of observation and personal experience of the life of plants. 

 And yet, however strongly our own minds respond to a desire 

 to believe this — it would be so clarifying — the obstinate "no 

 mechanism" objection stands boldly up to check our sympa- 

 thetic reasoning. 



Finally we should refer to the theories of heterogenesis or 

 species-forming by mutations or saltations, which have been 

 proposed at various times as a substitute for the theory of 

 species-forming by the gradual transformation through selec- 

 tion. During the discussion in the first few years after the 

 appearance of Darwin's "Origin of Species," the German zoolo- 

 gist von Kolliker expressed the belief that the change from 

 species to species would probably be found to be more sudden 

 and more distinctive than Darwin's theory permitted one to 

 assume. Later, the Russian botanist Korschinsky, on a basis 

 of general observation and some not very extensive personal 

 experimentation, definitely fornmlated a theory of species- 

 forming by heterogenesis which he placed strongly in contrast 

 with Darwin's theory of gradual transformation by selection, 

 which later theor}^ he claimed should be wholly given up. But 

 not until the publication of de Vries's \A'ork, Die Mutations-, 

 theorie, in which are recorded the results of close personal 

 observation and experimentation for twenty years on race and 



