VITAL ACTION VS. NATURE-ACTION 189 



may form the minor parts, the wings and flying but- 

 tresses, of social life, or the walls on which the super- 

 structures stand. For the better ways of construction 

 must ultimately yield the larger returns; and, con- 

 verselyj the actual products of a particular construc- 

 tive method must be a measure of its constructive right- 

 ness. 



I. Phylogeny 



Using this basic principle as our guide, we may 

 recognize two chief kinds of evolution: (i) the great 

 phylogenetic trunk lines which lead more or less di- 

 rectly upward from the lowest to the highest achieve- 

 ments in the plant and animal world; and (2) the nu- 

 merous collateral lines, or side branches, with their 

 countless ramifications which end in organisms on a 

 similar, or lower structural level. 



In the evolution of animal life, with which we are 

 here particularly concerned, it is not always easy to 

 distinguish these collateral lines from the main line of 

 evolution. But it is very important that we should be 

 able to do so, for the ways and means of progress util- 

 ized by the different classes of animals will have for 

 us the utmost scientific and moral value. They alone 

 can tell us why or how, the greater constructive powers 

 attained by man and his predecessors have been 

 achieved, and how we may best utilize that knowledge 

 for our future guidance. 



We have elsewhere 1 discussed this problem in a 

 technical way; we shall here briefly discuss some of 

 its broader aspects. 



'See "The Evolution of the Vertebrates and Their Kin." 



