DARWIN'S ALTERNATIVE EXPLANATION OF EVOLUTION. 55 



No changes occurred in the second to the fourth editions of the 

 " Origin " &c, but in the fifth (1869) he began to make the definite 

 variations rather more pronounced, as it followed the " Variation " 

 &c. (1868) , in which Darwin gives two collections of illustrations ; * 

 whereas he never gave a single instance to prove the truth of his 

 theory by means of natural selection among indefinite variations. 



The sixth and last edition of the " Origin " &c. was published in 

 1872. He has almost, so to say, saturated it with allusions to 

 definite variations by inserting new paragraphs and altering sentences, 

 even occasionally omitting the words " natural selection," as in the 

 following example : — " In a confined area . . . Natural Selection will 

 tend to modify all the individuals ... in the same manner." f 

 "In a confined area ... all the individuals varying in the right 

 direction" [i.e. "definitely"] "... will tend to be preserved "; J 

 that is, without any selection at all. The last sentence explains what 

 Darwin meant by " definite," in the passage where he draws the 

 distinction between it and indefinite. 



" By the term ' definite ' I mean an action of such a nature that 

 when many individuals of the same variety are exposed ... to any 

 change in their physical conditions of life, all or nearly all the indi- 

 viduals are modified in the same manner. A new sub-variety would 

 thus be produced without the aid of selection." § Herein we first 

 trace the recognition of a natural law as the rationale of self- 

 adaptation. 



The locus classicus for the two views is on the following page : 

 1* The direct action of the conditions of life, whether leading to definite 

 or indefinite results, is a totally distinct consideration from the effects 

 of Natural Selection ; for Natural Selection depends on the survival 

 under various and complex circumstances of the best fitted individuals, 

 but has no relation whatever to the primary cause of any modification 

 of structure." || 



Darwin intimated, as I quoted in my last lecture, that adaptations 

 were the most important feature of evolution requiring explanation. 

 Definite variations are practically, if not always, adaptations and are 

 the results of response. 



When did this idea of self-adaptation occur to Darwin ? He tells 

 us in his Autobiography : " I overlooked one problem of great im- 

 portance . . . viz. the tendency in organic beings descended from the 

 same stock to diverge in character as they become modified . . . the 

 solution is that the modified offspring of all dominant and increasing 

 forms lend to become adapted to many and highly diversified places in 

 the economy of nature."^ [My italics.] This " tendency," however, 

 can only be called into action by new and changed conditions of life. 



* Variation &c. ii. pp. 273, 277. 



f Origin &c. 1st ed. p. 104. If all the individuals vary aright, there 

 are none with " injurious " characters, and consequently there can be no natural 

 selection. 



% Op. cit. 6th ed. p. 80. § Variation &c. ii. p. 271. 



|| Op. cit. ii. p. 272. «[[ Life &c. i. p. 84. 



