74 ORGANIC EVOLUTION CONSIDERED 



The figure of a tree has been a favorite one by 

 which to represent the evolution of organic forms. 

 Beginning with primordial protoplasm as a seed, we 

 follow its growth. The main trunk of the tree, repre- 

 senting the direct line of man's ascent, is made up of 

 the countless forms that have intervened between 

 man and the first organism, the different races of 

 men being represented by an equal number of small 

 twigs at the top. As the primordial form multiplied, 

 it branched by favorable variations, the new forms 

 thus produced constituting branches of the tree of 

 evolution. Long before the authentic geological 

 record began, the tree of life divided into two great 

 divisions, — that of animals and that of plants, and 

 when the authentic record began we find animals, 

 widely different in structure, representing all the sub- 

 kingdoms and most of the classes of invertebrates. 

 And so the tree continued to grow and branch through 

 the ages, the individual twigs representing species and 

 varieties. 



If this tree were planted in the earth so that the 

 part under the earth would represent extinct forms, 

 and the part above the ground represent living forms, 

 it is evident that most of the tree would be buried, 

 for the reason that the living species are few com- 

 pared to the extinct. It is also evident that the 

 branches and twigs above ground, that represent liv- 

 ing forms, would, for the most part, stand isolated, 

 and that, to find their points of union, we must look 

 beneath the surface among extinct forms. If we 

 knew the entire record of life we could begin with 

 any species and trace it back, without a break, to the 

 primordial form. 



Having stated the general outline of the theory of 

 natural selection, I will present some of the argu- 



