24 BIOLOGICAL SOCIETY OF WASHINGTON. 



had been formerly attributed to the other agency ought not to 

 be credited to it instead ; and it cannot be denied that this in- 

 quiry tended to broaden the field of the selective at the ex- 

 pense of that of the functional principle. So clear and certain 

 are the workings of the former that it is considered safe to 

 credit it with every fact that can be explained by it, even 

 though it be also explicable by the other law. 



But it was not allowed to rest here. The difficulties in the 

 way of accounting for the transmission of qualities originating 

 after the birth of the parents appeared to some so great that 

 they began to doubt whether in fact such a thing is really 

 possible. Of course, there were many popular and superficial 

 writers on evolution who fail to distinguish the two principles 

 and talked as though all development was due to natural 

 selection, so that to the unscientific and popular mind evo- 

 lution and natural selection were largely synonymous and 

 vaguely comprehended, as is, in fact, still to a large extent, 

 the case. Other better informed people, including some 

 naturalists of note, were so dazzled by the new idea that they 

 lost sight of the old one, and habitually ignored the func- 

 tional element without criticising it or taking any account of 

 it. It appears to have been against this class that Mr. Her- 

 bert Spencer's brilliant exposition of the principle which, in 

 characteristic language, he calls "direct equilibration" was 

 directed. To this I shall have occasion to revert. 



For the present I propose to confine myself to those writers 

 who clearly comprehend the nature of the two principles, and 

 who either gravely doubt for what seem to them sufficient rea- 

 sons, or else deny altogether the efficacy of functional modifi- 

 cation and the doctrine of the transmission of acquired charac- 

 ters. The limits of an address such as this preclude any effort 

 to make the discussion historically exhaustive by enumerating 



