12 EVOLUTION AND GENETICS 



gives it a strength proportioned to the length of time of such use, 

 while the constant lack of use of such an organ imperceptibly 

 weakens it, causing it to become reduced, progressively diminishes 

 its faculties, and ends in its disappearance. 



"Second law: Everything which nature has caused individuals 

 to acquire or lose by the influence of the circumstances to which 

 their race may be for a long time exposed, and consequently by the 

 influence of the predominant use of such an organ, or by that of 

 the constant lack of use of such part, it preserves by heredity and 

 passes on to the new individuals which descend from it, provided 

 that the changes thus acquired are common to both sexes, or to 

 those which have given origin to these new individuals." 



To these he added later the idea that necessity in the organism 

 gives rise to new organs. Other corollaries expressed his belief 

 in various modifying factors, but essentially his theory involves 

 the belief that change springs from within the organism, in response 

 to definite conditions of the environment, and that such changes, 

 once initiated, are transmitted ])y heredity. The last point has 

 been a frequent subject of dispute, and was further complicated 

 because Lamarck added to these points the assumption that the 

 environment acted directly on plants. 



Saint- Hilaire was a contemporary of Lamarck who went back to 

 the belief of Buff on in the direct effect of environment. His chief 

 claim to distinction is that he believed in the occurrence of sudden 

 changes in organisms, giving rise to new species, an idea later 

 developed by deVries. 



Charles Darwin (1809-1882), (Fig. 2), is preeminent in the 

 field of evolutionary thought, as is well shown by the common use 

 of the word Darwinism as a synonym of evolution. While this 

 is an erroneous use of the term, his eminence is justified by his 

 works, not because he was the first man to believe in evolution as a 

 natural process, but because he brought to the support of the 

 theory so much evidence, accumulated and prepared with such 

 painstaking care, that he may rightly be termed the first to place 

 it upon an adequate and permanent foundation of scientific fact. 

 Since the appearance of his Origin of Species in 1859 there has been 

 no doubt among scientists of the reality of evolution as a process 

 in nature, although Darwin's theory of method has remained, 

 like all other such theories, a subject of dispute. His work 

 is essentially responsible for reforms in all fields of biology 



