No. 542] 



DARWIN'S THEORY OF EVOLUTION 



77 



tion of sentences and italicizing of important words, as 

 follows : 



• ... we have abundant evidence of the constant occurrence under 

 nature of slight individual differences of the most diversified kinds; and 

 we are thus led to conclude that species have generally originated by 

 the natural selection of extremely slight differences. This process may 

 be strictly compared with the slow and gradual improvement of the 

 racehorse, grayhound, and -amocock. As every detail of structure in 

 each species has to be closely adapted to its habits of life it will rarely 

 happen that one part alone will be modified; but as was formerly 

 shown, the co-adapted modifications need not be absolutely simultaneous. 

 Many variations, however, are from the first connected by the law of 

 correlation. Hence it follows that even closely allied species rarely or 

 never differ from one another by one character alone . . . from the 

 history of the racehorse, grayhound, gamecock, etc., and from their 



by a slow process of improvement ; and we know that this has been the 

 case with the carrier-pigeons as well as with some other pigeons. ... It 

 is certain that the ancon and mauchamp breeds of sheep, and almost 

 certain that the niata cattle, turnspit, and pug dogs, the jumper and 

 frizzled fowls, short-faced tumbler pigeons, hook-billed ducks, etc., sud- 



been with many cultivated plants. The frequency of these cases is 

 likely to lead to false belief that natural species have often originated in 



or at least of the continued procreation, under nature, of abrupt modi- 

 fication of structure, and various general reasons will be assigned 



Tims Darwin, on the admirable ground that no evidence 

 had been adduced in nature of such transformation, re- 

 jected the hypothesis of major saltatory evolution as 

 causing the natural appearance of entirely new types of 

 animals or plants or of entirely new and profoundly 

 modified organs. There was no evidence in 1872 and 

 there is none to-day of the sudden appearance m nature 

 of such a breed as the ancon sheep. On the other hand, 

 Darwin's meaning as to "slight individual differences of 

 the most diversified kinds/' as clearly conveyed in the 

 hundreds of observations he cited in "The Origin of 

 Species" (edition of 1872) and especially in his Varia- 

 tion of Animals and Plants Under Domestication," is 



