194 cook: evolution through normal diversity 



necessary as a means of referring definitely to the class of dif- 

 ferences which Meehan had described as "innate," "inherent," 

 and "coexistent with the species itself." In proposing the 

 name heterism additional examples were given, and the phenom- 

 enon was associated with more specialized forms of diversity 

 that are admitted generally to be independent of the environ- 

 ment, as sexes, castes, and dimorphic or pfflymorphic species.^ 



Darwin had made much of the agency of' insects in develop- 

 ing the highly specialized floral organs of orchids and other 

 plants, and such adaptive specializations had been accepted 

 as evidence that the environment, acting through natural selec- 

 tion, is the active agent in evolution. Meehan 's observations 

 and reasoning led to the opposite view, that crossing by insects 

 would tend to keep the species uniform, and would thus interfere 

 with evolution, instead of carrying it forward. To him it ap- 

 peared that special characters might develop more rapidly if 

 peculiar strains were kept separate, instead of being crossed 

 by insects. 



Efforts have been made to demonstrate the power of selec- 

 tion to induce changes of characters, but without finding any 

 consistent evidence. Progress appears to be made in cases 

 where the desired variations occur, but there is nothing to show 

 that variations in a particular direction can be induced by dint 

 of selection, after a pure-bred stock has reached a condition 

 of uniformity. vStatistical investigators often assume that 

 causal effects are demonstrated by proving that the average 

 of any particular character can be raised by selective elimina- 

 tion, but it remains to be shown that there is anything definitely 

 evolutionary in the shifting of averages. To hold logically 

 the idea that selection is the actuating cause of evolution, it 

 must be assumed that the selective elimination or cutting away 

 of one character or part of a species causes the other^ parts to 

 vary farther away from the selective stress, an assumption not 

 supported by definite evidence. 



Apart from the mutation theory, the alternatives of selective 

 causation of evolution are the Lamarckian idea of direct influence 



^ O. F. Cook. Aspects of kinetic evolution. Proc. Wash. Acad. Sci. 8: 244. 1907. 



