Summary and General Conclusions 463 



ronment, i.e. their structure and their responses are such that 

 they can live and leave descendants behind them. I can see 

 but two ways in which to account for this condition, either 

 (1) teleologically, by assuming that only adaptive variations 

 arise, or (2) by the survival of only those mutations that are 

 sufficiently adapted to get a foothold. Against the former 

 view is to be urged that the evidence shows quite clearly 

 that variations (mutations) arise that are not adaptive. On 

 the latter view the dual nature of the problem that we have 

 to deal with becomes evident, for we assume that, while the 

 origin of the adaptive structures must be due to purely 

 physical principles in the widest sense, yet whether an organ- 

 ism that arises in this way shall persist depends on whether 

 it can find a suitable environment. This latter is in one 

 sense selection, although the word has come to have a differ- 

 ent significance, and, therefore, I prefer to use the term 

 survival of species. 



The origin of a new form and its survival after it has 

 appeared have been often confused by the Darwinian school 

 and have given the critics of this school a fair chance for ridi- 

 culing the selection theory. The Darwinian school has sup- 

 posed that it could explain the origin of adaptations on the 

 basis of their usefulness. In this it seems to me they are 

 wrong. Their opponents, on the other hand, have, I believe, 

 gone too far when they state that the present condition of 

 animals and plants can be explained without applying the 

 test of survival, or in a broad sense the principle of selection 

 amongst species. 



It will be clear, therefore, in spite of the criticism that I 

 have not hesitated to apply to many of the phases of the selec- 

 tion theory, especially in relation to the selection of the indi- 

 viduals of a species, that I am not unappreciative of the great 

 value of that part of Darwin's idea which claims that the con- 

 dition of the organic world, as we find it, cannot be accounted 

 for entirely without applying the principle of selection in one 



