special Evolution Theories 293 



for both the progressive appearance of new forms and the 

 constant fact of the fitness of hfe to the existing conditions. 

 An innate principle making for perfection has also been 

 suggested, but in the minds of most people this approaches 

 too close to mysticism to be of value as an element in a 

 scientific theory. 



If there is to be transmutation of species, there must be 

 variation. Variation had been observed from early times, 

 and has been taken for granted as the raw material of evolu- 

 tion by many thinkers. Darwin, in developing the princi- 

 ple of natural selection, realized the importance of variation 

 but did not make it his business to find out how variations 

 come about. Nor did he distinguish clearly and consistently 

 between variations that fluctuate with changing conditions 

 and those that are transmitted. Lamarck attributed cer- 

 tain kinds of variations to the direct action of the environ- 

 ment upon the individual, and others to the inner action 

 in response to external stimulation. He assumed also that 

 variations of the latter kind are transmitted to the offspring. 

 It was only after the study of heredity had made consider- 

 able advance that the distinction between inherited and non- 

 inherited variations came to be emphasized as important, in 

 the theory of evolution. By the end of the Nineteenth 

 Century scientists were prepared to consider as a basis of evo- 

 lution the appearance of saltations or jumps — individuals 

 that depart in a definite way from the parental type and 

 transmit their distinctive characters to their offspring. The 

 more intensive study of the mechanism of heredity has given 

 rise to theories about the origin of heritable variations 

 through some process which affects directly the germinal 

 substance or the chromosomal material. 



Until our own time there were no thoroughgoing the- 

 ories of heredity that could help clarify the facts of trans- 

 mutation. Everybody knew that like begets like, but there 

 were not enough facts at hand to suggest even a remote ap- 

 proach to the mechanism. Francis Galton, a cousin of 

 Charles Darwin, had gathered a large mass of material for 



