AGENCIES, HABITAT, AND GROWTH 109 



But evolution cannot be uniformly progressive, for 

 organic innovations have widely different creative 

 values, and produce widely different rates of growth, 

 giving rise to that deceptive appearance of discon- 

 tinuity which leads us to classify events or objects into 

 larger or smaller categories according to the degree of 

 their resemblance. 



After making due allowance for irretrievable losses, 

 and for our fragmentary knowledge, it is still evident 

 that the things we are trying to express in our classi- 

 fications are these very differences in the rate of con- 

 structive action, upon which the rate of evolution de- 

 pends. In others words, the unequal creative values 

 of the various improvements in organic service are the 

 punctuation marks in nature-growth, and the cause of 

 its creative cadence. The periods of more rapid pro- 

 gress, which follow after these improvements, appear, 

 in perspective, as larger or smaller gaps in the flow of 

 creative events. The more stable cooperative read- 

 justments give visible expression to the more enduring 

 anatomical characters which are the distinguishing 

 marks of species, genera, classes, etc. 



For that reason, every large class of animals is 

 necessarily separated from its nearest of kin by what, 

 to the discriminating eye of the morphologist, may ap- 

 pear to be a wide structural gap. But, on analysis, it 

 is seen that the real difference is not in itself a large 

 one, although it is always a highly cooperative one, 

 carrying with it, of necessity, a multitude of other 

 changes. 



Whenever, therefore, the right ways, or better, or 

 more serviceable ways, of conveyance are worked out, 

 or "happen" more growth and higher levels of devel- 



