194 THE PROBLEMS OF EVOLUTION 



are not the initial stimulus for change, the environ- 

 ment comes to the fore as the initiating cause of 

 evolution. 



Nothing is so strongly indicative of this fact as 

 the abundant evidence of organic constancy fur- 

 nished by modern genetics. The organisms with 

 which we must now work have heritages so stable 

 that their absolute permanence has been seriously 

 proclaimed, and yet the most serious supporters 

 of this view have been, at the same time, the most 

 vigorous proponents of the idea that change must 

 emanate from the heritage. This anomalous situa- 

 tion has nothing to support it. The heritage tends 

 to maintain itself and does so to a remarkable 

 degree. As it now exists it is an extremely variable 

 factor which may give rise through recombination 

 of its many components to new or previously un- 

 known conditions in individuals, but the explana- 

 tion of its variability is one of the tasks of biology. 

 Its failure to be completely invariable must have 

 adequate cause, and with a complex and variable 

 environment inevitably associated with it, it seems 

 utterly useless to seek change in the one factor 

 which tends to be constant. 



Anent this matter, Osborn has recently written 

 as follows: ''Finally, and perhaps from glandular 

 impulses (Keith), phylogeny proves that independ- 

 ent of selection, of environment, of habit, certain 

 phyla exhibit rapid or accelerated physical and 



