The Biochronic liquation. 665 



ment far better than tliat theory. We now sec that when 

 appHed to the great problems of hfe it is free from 

 those insuperable difhcnlties, which so many investigators 

 have found to stand in the way of the theory of selec- 

 tion. 



The theory of selection demands almost unlimited 

 time for the evolution of organisms; for the mutation 

 theory, on the other hand, the time which the physical 

 geologists grant to life, is amply sufficient. Idiis view 

 was first clearly expressed by Brooks, in accordance with 

 Huxley, when he showed that all the difficulties which 

 beset the theory of selection and which, according to 

 many investigators, needed 2,500,000,000 years for the 

 whole process of evolution, would disappear if we assume 

 relatively sudden and discontinuous changes to take place 

 from time to time.-^ 



The most distinguished investigators demand a period 

 of about 24 million years, to cover the duration of life 

 on the earth. If the ancestors of our Oenothera La- 

 inarcklana have produced, once in ever}^ 4000 years, a mu- 

 tation which made them richer by a single character, our 

 plant would now be composed of 6000 such characters, 

 a number far higher than comparative and systematic 

 science can by any means accumulate in its description. 



This rough calculation shows at any rate that the 

 demands made by the theory of mutation are not so exor- 

 bitant as those made by that of selection. Neither the 

 number of mutation periods passed through, nor that of 

 the characters acquired in them, is beyond our powers 

 of comprehension. On the contrary the phenomena 

 viewed from this standpoint are such that they indicate 

 the possibility of a much closer investigation. 



^W. K. Brooks, loc. at., p. 286. 



