528 PATTEN— COOPERATION AS A FACTOR IN EVOLUTION. 



portance. The great cooperative value of these improvements led to 

 the rapid expansion and the readjustment of other organs expressed 

 in the term evolution, and the increased rate with which these events 

 follow one another is perhaps the chief reason for the large gap, in 

 retrospect, between the vertebrates and their more immediate arach- 

 nid ancestors. 



V. 



The special cases above cited are peculiar only in the magnitude of 

 their ensuing results. The principles involved are universal. It is 

 because the rate of evolution and the creative value of its products 

 vary greatly from time to time and place to place, that there is any 

 real basis, historic and vital, for classification. It is this historic 

 process and its sequence of causal conditions that our systems of 

 classification tend to portray more and more fully. 



Classification is not merely the arrangement of animate and in- 

 animate things according as they are hke or unlike, any more than 

 history is a mere record of events. 



Classification is history in tabloid form, and there is little value 

 in either one or the other if they do not in some measure express 

 the change of pace and direction of evolution and the creative value 

 of the innovations that produced them. 



There would still be great epochs in history, however complete 

 the records might be ; for the same reason, the transition from a 

 lower class of animals to a higher one will always appear, in retro- 

 spect, as a relatively large gap, marked by the appearance of a few 

 cooperative characters of small magnitude in themselves, but of 

 great creative value. 



A familiar example of this principle is seen in the transition from 

 fishes to amphibia, where the chief event was the apparently insig- 

 nificant enlargement and short-circuiting of one of the branchial 

 blood vessels. This event ultimately led to the substitution of lungs 

 for gills, and to many other changes of far reaching importance in 

 the internal and external administration of their lives. 



The four chambered heart ; the hot, even tempered blood ; pla- 

 cental nutrition; and articulate speech, are other examples of those 

 incidental products of growth, whose appearance is epoch-making 



