304 O. F. COOK 



evolution might be described as organic change or motion, but 

 it is not safe to assume the converse, that any and all organic 

 changes represent evolution. Degeneration is quite as general 

 a phenomenon as evolution, and the two are easily confused. 



EFFECTS OF SEGREGATION. 



Many discussions of evolution rest upon abstract terms which 

 have no concrete meaning or definite application. Such ex- 

 pressions as -prepotency and reversion are veritable stumbling- 

 blocks in the evolutionary theories of those who use the words 

 without taking into account the different relations of the phe- 

 nomena grouped under them. Having once made the assump- 

 tion, for example, that mutations are instances of a normal 

 saltatory evolution, it is natural to look upon the prepotency 

 which brings "reversion" as tending to prevent evolutionary 

 progress by "the swamping effects of intercrossing," of which 

 the last decades have heard so much. Segregation appears 

 essential for the preservation of new characters ; it becomes, in 

 other words, a primary factor or condition of evolution. This 

 series of deductions leads, however, to a biological absurdity, 

 because extreme segregation or inbreeding not only puts an end 

 to true evolutionary advance, but causes the deterioration of the 

 organisms themselves. 



The phenomena which have been interpreted as mutations 

 and reversions can be accommodated under a kinetic theory of 

 evolution without this fatal inconsistency of inference. Instead 

 of affording progressive new characters, or constituting new 

 species, there are reasons for believing that mutations are 

 digressive lapses from normal heredity, induced by inbreeding 

 or too great segregation. The '* prepotency of the wild type" 

 which " swamps " these abnormalities is not a backward step 

 along the highway of evolutionary progress. It marks, instead, 

 a return from a too narrow sidepath. The reversion is only 

 formal ; it represents a restoration rather than a retrogression. 



Evolution has seemed to go backward only because the side- 

 path has been mistaken for the main thoroughfare. The pre- 

 potency which seems to obliterate the mutational " new species" 

 is the same which carries forward the evolutionary progress of 



