Darwin, and after Darwin. 



gained of their logical connexion with this primary 

 point of difference. 



The theory of Natural Selection 

 according to Darwin. 



Natural Selection has been 

 the main means of modifica- 

 tion, not excepting the case of 

 Man. 



(a) Therefore it is a question 

 of evidence whether the La- 

 marckian factors have co- 

 operated. 



(6) Neither all species, nor, 

 a fortiori, all specific char- 

 acters, have been due to 

 natural selection. 



(f) Thus the principle of 

 Utility is not of universal ap- 

 plication, even where species 

 are concerned. 



(</) Thus, also, the sugges- 

 tion as to Sexual Selection, or 

 any other supplementary cause 

 of modification, may be enter- 

 tained ; and, as in the case of 

 the Lamarckian factors, it is a 

 question of evidence whether, 

 or how far, they have co- 

 operated. 



(e) No detriment arises to 

 the theory of natural selection 

 as a theory of the origin of 

 species by entertaining the 

 possibility, or the probability, 

 of supplementary factors. 



(/) Cross-sterility in species 

 cannot possibly be due to 

 natural selection. 



Thetheory of Natural Selection 

 according to Wallace. 



Natural Selection has been 

 the sole means of modification, 

 excepting in the case of Man. 



(a) Therefore it is ante- 

 cedently impossible that the 

 Lamarckian factors can have 

 co-operated. 



(b) Not only all species, but 

 all specific characters, must 

 necessarily have been due to 

 natural selection. 



(c) Thus the principle of 

 Utility must necessarily be of 

 universal application, where 

 species are concerned. 



(d) Thus, also, the sugges- 

 tion as to Sexual Selection, or 

 of any other supplementary 

 cause of modification, must be 

 ruled out ; and, as in the case 

 of the Lamarckian factors, 

 their co-operation deemed im- 

 possible. 



(e) The possibility and, a 

 fortiori the probability of any 

 supplementary factors cannot 

 be entertained without serious 

 detriment to the theory of 

 natural selection, as a theory 

 of the origin of species. 



(/) Cross-sterility in species 

 is probably due to natural 

 selection 1 . 



1 This, to the best of my judgement, is the fairest extract that I can 

 give of Mr. Wallace's most recently published opinions on the points in 



