2 Introductory [ch. 



the evolution of species that the facts have hitherto been 

 most profitably investigated. It was in the attempt to 

 ascertain the interrelationships between species that experi- 

 ments in genetics were first made. The words ''evolution " 

 and " origin of species " are now so intimately associated 

 with the name of Darwin that we are apt to forget that the 

 idea of a common descent had been prominent in the minds 

 of naturalists before he wrote, and that, for more than half 

 a century, zealous investigators had been devoting them- 

 selves to the experimental study of that possibility. Promi- 

 nent among this group of experimenters may be mentioned 

 Koelreuter, John Hunter, Herbert, Knight, Gaertner, Jordan, 

 Naudin, Godron, Lecoq, Wichura — men whose names are 

 familiar to every reader of Animals and Plants under 

 Do7nestication. If we could ask those men to define the 

 object of their experiments, their answer would be that they 

 were seeking to determine the laws of hereditary trans- 

 mission with the purpose of discovering the interrelationships 

 of species. In addition to the observation of the visible 

 structures and habits of plants and animals they attempted 

 by experiment to ascertain those hidden properties of living 

 things which we may speak of as genetic, properties which 

 breeding tests can alone reveal. The vast mass of 

 observation thus accumulated contains much that is of 

 permanent value, hints that if followed might have saved 

 their successors years of wasted effort, and not a few 

 indications which in the light of later discovery will greatly 

 accelerate our own progress. 



Yet in surveying the work of this school we are 

 conscious of a feeling of disappointment at the outcome. 

 There are signs that the workers themselves shared this 

 disappointment. As we now know, they missed the clue 

 without which the evidence so laboriously collected remained 

 an inscrutable medley of contradictions. 



While the experimental study of the species problem 

 was in full activity the Darwinian writings appeared. 

 Evolution, from being an unsupported hypothesis, was at 

 length shown to be so plainly deduclble from ordinary 

 experience that the reality of the process was no longer 

 doubtful. With the triumph of the evolutionary idea, 

 curiosity as to the significance of specific differences was 



