THE RAW MATERIALS OP EVOLUTION 123 



the year by giving them fattening food and keeping 

 them without much exercise in dim light. Gradual 

 return to the light and the addition of mealworms 

 to the menu brought back the spring song, even 

 in mid-winter. After a year, and at the beginning 

 of the normal breeding season, individual tanagers 

 and bobolinks were gradually brought under normal 

 conditions and activities, and in every case they 

 moulted from nuptial plumage to nuptial plumage, 

 the duU colours of the winter season having been 

 skipped. The inherited constitution determines 

 what is possible, but there is evidently a large 

 range of plasticity. We do not know that modifica- 

 tions are entailed, but we must attach all the more 

 importance to the influence of the environment in 

 bringing about individual adjustment, in stimu- 

 lating variation, and in punctuating developmental 

 processes. 



Relation to Human Life. — What has all this 

 discussion regarding fluctuations and variations 

 and mutations and modifications to do with 

 human life ? It would be easier to answer this 

 question if we knew more about these changes, 

 but some practical considerations are obvious. 



To begin with, man probably arose by a mutation ; 

 that is to say, by a discontinuous variation of 

 considerable magnitude. Every one who has known 

 a genius has in this happy experience some idea of 

 what is meant by a mutation, though the com- 

 parison breaks down inasmuch as the quality of 

 genius is rarely heritable. It is not merely that 

 the genius has more brains ; he has a new pattern 

 of brains, and a large mutation is a new constitu- 

 tional pattern. It is likely that man had his 

 starting-point as a prepotent anthropoid genius. 



