414 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



that there is nothing left to be explained in the living world, that there 

 is no door leading to the secret chambers of nature to which natural 

 selection is not an 'open sesame ' " (13). 



So, too, in discussing sexual selection, which " remains to-day 

 practically where Darwin left it," " this neglect affords an example 

 of the baneful results of the too-ready acceptance of an enticing theory. 

 ' Natural selection explains everything, why then investigate further ? 9 

 seems to be the general attitude of our present day naturalists " (308). 

 Similarly they have neglected the subject of "correlation " for the same 

 reason (358). 



When we try to find the authors' view with regard to natural selection, 

 they first say : " We recognize the strength and the weakness of the 

 Darwinian theory " (27) ; but they add : " It is incumbent upon us to 

 prove our assertion that it does not afford an adequate explanation of all 

 the varied phenomena observed in the organic world" (30). Yet they 

 add : " There is no room for doubt that natural selection is a factor in 

 the making of species" (34). 



The next point for inquiry is. What are the authors' views on varia- 

 tions, upon which natural selection is supposed to act ? 



Darwin, they remind us, "makes no attempt to explain variation" 

 (35). They rightly observe that " the double assumption that variations 

 are for all practical purposes haphazard in origin and indefinite in direc- 

 tion is necessary if natural selection is to be the main factor in evolution. 

 For if variations be not haphazard, if they are definite, if there be a 

 directive force behind them . . . then selection is not the fundamental 

 cause of evolution " (53). 



The authors, at this point, call attention to Darwin's later views, in 

 which he strongly emphasizes "definite variations." These will be found 

 in his " Animals and Plants under Domestication," vol. ii. pp. 250, 253, 

 256, 271 ; and " Origin," 6th ed. He attributes all variations to the 

 "direct action of changed conditions of life." The results are (he says) 

 either "indefinite" or "definite." If the former, then natural selection 

 must be called in ; if the latter, then it is not required, as all the indi- 

 viduals vary in adaptation. And although, if there be too many to live, 

 the stronger may oust the weaker, yet all changed in adaptation, there 

 are no " inadaptive "or " injurious " variations at all ; unless malforma- 

 tions, arrested developments, like " pink eyes, &c, are to be reckoned as 

 variations." Then these will probably always die in the struggle for life. 

 Apart from such r Nature makes no such mistakes as to produce indiscrimi- 

 nate or indefinite variations. There is, in fact, no such alternative as 

 Darwin thought. 



Darwin did not, therefore, in later life "contradict himself" or 

 " scarcely know his own mind " (54) ; or say that " definite variability is 

 far less important than indefinite " (55), though in the first edition of 

 the " Origin " this last statement is true, as stated in the Preface ; but 

 in 1876 he considered it the "greatest mistake" he had made to have 

 overlooked the importance of definite variations (letter to Wagner). 



Let us now come to the distinction between continuous and discon- 

 tinuous variations, which are now called mutations, sports, or well- 

 marked and suddenly appearing differences, which may be hereditary. 



