2 THE GROWTH OF GROUPS 



direction ; but in so doing he deceives only himself, to the 

 critical reader his personal conviction or bias is obvious 

 from the first. It is well, therefore, to admit at the outset 

 that this book is written in the factional spirit as an 

 expression of opinion, derived mainly from the writings 

 of others but supported by personal observation. 



Darwin has said, " We have no evidence of the appear- 

 ance or at least of the continued procreation, under 

 nature, of abrupt modifications of structure." These 

 words call attention to the fact that abrupt modifications 

 may occur ; in other words, that an offspring may possess 

 some definite and obvious quality or qualities which were 

 not possessed by its parents. Furthermore, the words 

 " under nature " remind us that such modifications may 

 be propagated continuously under man's protection. 

 Several races of domestic animals and plants are known 

 to have arisen abruptly from sports. 



It seems, however, that Darwin's conviction as to 

 the inefficacy of sports was unsettled, for in the sixth 

 edition of " The Origin of Species " there appears the 

 following well-known passage. "... variations which 

 seem to us in our ignorance to arise spontaneously. It 

 appears that I formerly underrated the frequency and 

 value of these latter forms of variation, as leading to 

 permanent modifications of structure independently of 

 Natural Selection." Besides the admission they contain, 

 these words are interesting as showing that gradual change 

 should be looked upon as the essential condition of Evo- 

 lution by Natural Selection. A race arising from a sport, 

 in captivity or under nature, would occur independently 

 of selection, as that process was conceived by Darwin. 

 To speak of selection among mutants is to change the 



