THE AMERICAN NATURALIST [Vol. XL V 



those that are strong and multiply rapidly. Thus many 

 of the combinations produced are canceled; only the 

 strongest combinations survive. We have then on a 

 most extensive scale an operation in natural selection 

 and the survival of the fittest; the production of many 

 combinations, some of which survive, while others fail. 

 As already set forth, there is some indication of the same 

 process in the case of conjugation within the genotype. 



At our last meeting I tried to summarize the facts as to 

 the relation of genotypic investigation to selection; it 

 turned out that much which had been deemed a progres- 

 sive action of selection was not such; and up to that time 

 the action of selection in modifying genotypes had not 

 been demonstrated. Similarly, I had earlier summar- 

 ized the facts regarding selection in behavior, showing 

 that it there plays a large part. I have hence suffered 

 the peculiar fate of being belabored as an anti-selectionist 

 in genetics, while subjected in the field of behavior to 

 rough treatment as the champion of selection. What I 

 tried to do in both cases was, to determine how far we had 

 actually seen the effectiveness of selection — holding this 

 question quite apart from what we believe must occur, or 

 believe will be found to occur when we have seen it. It 

 appeared clear, and still appears clear, that a very large 

 share of the apparent progressive action of selection 

 has really consisted in the sorting over of preexisting 

 types, so that it has by no means the theoretical signi- 

 ficance that had been given to it. When operating on a 

 single isolated type it appeared that the progressive 

 action of selection had not been seen. These are facts of 

 capital importance to the experimenter; besides their 

 theoretical significance, they open to each of us the oppor- 

 tunity to direct our efforts upon precisely this point, and 

 so perhaps to be the first to see examples of this funda- 

 mental process not yet seen. I hoped to accomplish this 

 myself, but after strenuous, long-continued, and hopeful 

 efforts, I have not yet succeeded in seeing selection effec- 

 tive in producing a new genotype. This failure to dis- 

 cover selection resulting in progress came to me as a 



