120 REDUCTION OF VARIABILITY. 



homozygous will continue to exist so long as multiplication is 

 unchecked. But, wherever the group is continued from a 

 fraction of the number of individuals, or where a colony is 

 started by a few individuals, the chance of the heterozygotes 

 to be included in the group, or to have heterozygous children 

 included, is proportionate to their frequency. Heterozygotes 

 will produce homozygotes, but not the reverse. 



The group of organisms chosen by fate to become the parents 

 of the next generation is usually, but always occasionally, con- 

 siderably smaller than the number of individuals of their spe- 

 cies. Every case in which rare individuals, having genes, not 

 present in the majority, or in which rare individuals being im- 

 pure for, or lacking in genes, common property of the major- 

 ity, happen to be excluded from the number of pro-creating 

 individuals, the total potential variability is lowered. 



This, in our opinion, is the most important gain in knowledge 

 which we owe to Mendel's work, and to the biomechanical 

 interpretation of his work. Reduction of potential variability, 

 in other words purity of species is automatic, and not depend- 

 ant upon any sort of selection. Darwin lacked the necessary 

 key at the time when he needed it most, and when he came 

 into touch with Wagner's work, it could not shake his faith in 

 selection as the cause of stability of species. All the recent 

 work in Genetics, Mendel's law, the things we have since 

 learned about the nature of the genes, the selection experiments 

 with the most diverse material, have shown us that Wagner 

 in opposing Darwin in this fundamental point had the right 

 wholly on his side. 



From the way Darwin reacted upon the work of Naudin 

 and Wagner, and from the slight impression Mendel's work 

 made upon Darwin's greatest pupil, Weismann, we are able to 

 see why it did not seeme of great importance to Charles Dar- 

 win. But it would appear to me that Wagner would have 

 greatly appreciated it, and could have been trusted to incorpo- 

 rate it into a really logical evolution-theory. 



In every single instance in which the proportion of individ- 



