Ill 



THEORIES OF EVOLUTION 



An Address delivered to the Boston Society of Natural History, as 

 an Introduction to the Discussion, held on February 7, 1894. Reprinted 

 from the Proceedings of the Society, vol. xxvi, p. 327. 



Revised ; additional footnotes. 



In dealing with theories of evolution, I think that we 

 shall all be agreed that we may leave out of consideration 

 the question of the origin of life, and deal only with 

 what has happened to life after its appearance, however 

 that may have taken place. On this subject we shall 

 probably most of us still agree with the opinion of 

 Darwin 1 , that we are not in a position to even speculate 

 or think upon that question, — that any speculation about 

 it is almost a waste of time. And this, I think, remains 

 .me in spite of the magnificent results of the organic 

 chemists in producing chemical bodies by synthesis, 

 which before had been regarded as capable of being 

 made only in the laboratory of the living body. Many 

 of these can now certainly be produced, but that is very 

 different indeed from creating protoplasm endowed with 

 life ; and so far are we from achieving this by any 

 chemical means that I think we may venture to dismiss 

 all consideration of the ultimate origin of life. 



But granting the origin of living matter, these theories 

 of evolution which we are considering and hope to discuss 

 to-night can deal with it, and with their help we believe 

 that we can account for what has subsequently happened ; 

 namely, the evolution of all forms of life, animal and 

 vegetable, upon the surface of the earth. 



The first of these theories which I propose to discuss 

 is the well-known Darwin-Wallace theory of Natural 

 Selection, with its three factors. 



First, Individual Variation, — the fact that individuals 

 differ, and that the differences are essential or inherent 



1 In Life and Letters. 



