2 82 GENERAL BIOLOGY 



records of palaeontology. Many definite lines of specializa- 

 tion, manifestly independent of environing conditions, are 

 traceable among fossils, and some of these lines of specializa- 

 tion may be followed out to their final end. Useful struc- 

 tures, such as in their beginnings natural selection might 

 have favored, have been developed far beyond their optimum, 

 and their possessors have disappeared from the earth. 

 Famous examples are the sabre-toothed tigers and the 

 Irish elk. The canine teeth of the sabre-toothed tiger were 

 so over developed as to be useless, their tips projecting out- 

 side the mouth when opened; and the antlers of the Irish 

 elk attained such size and weight as to be a very great 

 encumbrance. Well developed canine teeth are manifestly 

 advantageous for tearing prey, and all carnivorous mam- 

 mals have them; and strong horns for meeting rivals in 

 combat, are advantageous too, and the males of most social 

 ruminants have them ; but in both cases the good thing was 

 overdone ; specialization far outran utility. 



We need not go so far afield for illustrations of develop- 

 mental tendencies that have exceeded utilitarian demands. 

 The studies of floral structures in Chapter I should have 

 brought us into contact with numerous examples. What 

 possible use is there for all the complicated apparatus of 

 the milkweed or the orchis flower? or for all the arching, 

 scalloping, and fringing of the lips of a mint flower? Clearly 

 the living substance has inherent powers that manifest them- 

 selves in racial tendencies, independently of outward mold- 

 ing forces, and that sometimes are not amenable thereto. 



We may perhaps conceive of orthogenesis as a manifesta- 

 tion of a sort of developmental inertia. A genetic tendency, 

 once set going, tends to keep going in a straight line. How 

 it starts we do not know. Natural selection may have 

 something to do with its survival in the beginning, but 

 evidently cannot stop it at the point of optimum develop- 



