ORGANIC EVOLUTION 281 



tions of whatever sort or origin, furnish the materials 

 of progress, and the competition of life, when of eliminative 

 severity, "selects" the fittest variants for survival, chiefly 

 by the elimination of the less fit. Real selection involves a 

 psychic factor; it may occur if, for example, birds select the 

 most luscious wild cherries or other fruit, whose seeds they 

 carry to a place favorable for growth ; or if insects select the 

 showiest of the flowers whose pollen they distribute. 



Natural selection is thus seen to be an explanation of the 

 modus operandi of those extrinsic forces that tend to make 

 every race conform to conditions of environment. With 

 the intrinsic forces of the living organism, it can only 

 indirectly deal. Natural selection does not, therefore, 

 account for the origin of anything new among organisms, 

 but only for the preservation of such new things as are 

 heritable, advantageous and fit. Nevertheless, it is at this 

 day the one process of evolution whose operations are 

 clearly set forth. 



Orthogenesis. — By this name we designate a racial ten- 

 dency toward some one particular line of development : an 

 innate tendency, uncontrolled by external conditions. 

 Such racial development is not fortuitous, but in a single 

 direction, straight ahead, as the name indicates. But 

 orthogenesis is not an explanation of a process; it is merely 

 a name for one. 



The orthogenetic tendency is manifest in its incipiency 

 when a group of organisms tends to vary strongly in the 

 direction of some one particular structural type ; when the 

 variations are not promiscuous (indeterminate) but show a 

 strongly marked 'trend. This is illustrated by the inherent 

 odd-pinnateness of the compound leaves of the sumacs; 

 and equally well by the inherent abrupt-pinnateness of che 

 leaves of the cassias (partridge pea, etc.) It is best illus- 

 trated by the actual history of races as revealed by the long 



