314 O- F. COOK 



vert" to the normal t3^pe of their own species, through inter- 

 crossing. It may be admitted, perhaps, that a mutation is as 

 near as an3'thing to the original idea of reversion ; it is at least 

 a ^/version, an evolutionary aberration, or wandering aside. 

 But in this sense reversion becomes synonymous with muta- 

 tion, and is thus a superfluous term, as well as inappropriate. 

 It is equally at variance with the current meaning of the word 

 to refer to the recovery of the normal form of the species as re- 

 version, since this process is conservative and reconstructive 

 rather than degenerative or retrogressive, however much an 

 " improved" breed may appear to " deteriorate" when crossed 

 with its wild or less inbred relatives. If this be reversion the 

 word should be relieved of all sinister implications, at least in 

 evolutionary usage. 



Better than the substitution of a new term for " reversion" 

 would be the transfer of emphasis from this negative concept 

 to the kinetic view of prepotency, not in the Mendelian sense of 

 an arbitrary and inexplicable "dominance" of one character 

 over another, but mindful of the law of proportion between 

 symbasis and prepotency, without which the facts of descent are 

 a hopeless tangle of apparent contradictions. The -prefotcncy 

 of a variation defends upon the extent 0/ the normal interbreed- 

 ing under which it arises. The law of mutation is the biological 

 converse : As the lines of descent are narrozved the amplitude 

 of variations increases and reproductive fertility declines. 



PREPOTENCY ILLUSTRATED BY PARALLEL VARIATION. 



The abnormality of mutations is scarcely to be appreciated 

 without a recognition of the normal diversity (heterism) of the 



species which had not been introduced into the United States at the time when 

 the cross Avas made. 



The same phenomenon occurs among human hybrids. Mulattos are some- 

 times very black, and sometimes white. Wallace observed in the Portuguese 

 settlements of the Malay Archipelago that the mixed population has " become 

 darker in color than either of the parent stocks," and in ]?ia/il that crosses be- 

 tween Portuguese and Indians are " not infrequently lighter tlian citlicr parent." 

 (The Malay Archipelago, p. 257.) 



"Another clear fact is the rapid loss of resemblance of the offspring to the 

 Indian parent, the white element always predominating; the aboriginal seems 

 to be merged into the Spanish in Iavo generations." (Orton, The Andes and 

 Amazon, 3d Edition, 465.) 



