1 40 CREATIVE EVOLUTION CHAP. 



siderable number of appendages, each of which has 

 its special function. In the vertebrates, activity is 

 concentrated in two pairs of members only, and these 

 organs perform functions which depend much less 

 strictly on their form. 1 The independence becomes 

 complete in man, whose hand is capable of any kind ot 

 work. 



That, at least, is what we see. But behind what 

 is seen there is what may be surmised two powers, 

 immanent in life and originally intermingled, which 

 were bound to part company in course of growth. 



To define these powers, we must consider, in the 

 evolution both of the arthropods and the vertebrates, 

 the species which mark the culminating point of each. 

 How is this point to be determined ? Here again, 

 to aim at geometrical precision will lead us astray. 

 There is no single simple sign by which we can 

 recognize that one species is more advanced than another 

 on the same line of evolution. There are manifold 

 characters, that must be compared and weighed in each 

 particular case, in order to ascertain to what extent they 

 are essential or accidental and how far they must be 

 taken into account. 



It is unquestionable, for example, that success is the 

 most general criterion of superiority, the two terms 

 being, up to a certain point, synonymous. By success 

 must be understood, so far as the living being is con 

 cerned, an aptitude to develop in the most diverse 

 environments, through the greatest possible variety of 

 obstacles, so as to cover the widest possible extent of 

 ground. A species which claims the entire earth for 

 its domain is truly a dominating and consequently 



1 See, on this subject, Shaler, The Individual, New York, 1900, pp 

 118-125. 



