EVOLUTION AND MUTATION 



In the beginning of the last century Lamarck founded 

 the theory of a common descent for all living beings. It 

 afforded him the only possible means of explaining system- 

 atic affinity. He assumed that the influence of the en- 

 vironment was capable of changing the characters of the 

 organisms, and of fitting them for their life conditions. His 

 evidence, however, was very scanty and therefore he failed 

 in convincing his contemporaries. 



Half a century afterward Darwin brought together such 

 .an overwhelming mass of evidence that opposition had to 

 give in. His main point was one of comparative investiga- 

 tion. At his time it was universally assumed that species 

 had been created as such, but that subspecies and varieties 

 had been derived from them according to natural laws. 

 Darwin proved that no such distinction between species 

 and subspecies exists. Their marks are of the same nature, 

 and if a natural origin is assumed for one group, it must be 

 conceded for the other too. The same holds good for genera 

 and families, and even for the higher divisions of the system. 



Moreover, Darwin showed that the sequence of the 

 appearance of organisms during geological times finds a 

 natural explanation on the assumption of the theory of de- 

 scent, and that the geographical distribution of animals and 

 plants is exactly as we should expect it to be if their common 

 origin were the main factor in assigning them their special 

 domains. 



These broad proofs of the theory of evolution are quite 

 independent gf the question by which means and in what 

 way new species are produced from the existing ones. This 

 question, however, appeals more directly to the imagination, 



