168 MODES OF RESEARCH IN GENETICS 



times been forgotten. It is difficult to remember 

 always that a law of nature may be presumed to 

 have been in operation before its discovery. If 

 Mendel's law represents a real and fundamental 

 law of nature, as certainly appears to be the case in 

 the light of present evidence, it is quite certain 

 that it did not begin operation in a.d. 1900. 

 Whatever of success has been attained during 

 centuries past in the breeding of improved strains 

 of animals and plants must have been attained by 

 methods and practices which were not violently 

 in discord with Mendelian principles. A nomad 

 Arab may never have heard of the principle of 

 segregation, but none the less he had to reckon 

 with the phenomenon in breeding his horses. 



Looking at the matter in this way, the reason 

 is clear why the rediscovery of Mendel's work and 

 the brilliant genetic researches which have fol- 

 lowed did not and could not have had any pro- 

 found revolutionary effect on the practice of the 

 animal breeders' art. By years — even centuries 

 — of *' trial and error " methods, breeding practice 

 has been brought into rather close conformity 

 with the basic laws of heredity. The discovery 

 of some of these laws by the geneticist could not 

 radically change the breeder's way of attaining 

 results. 



What then has the rapidly developing science of 

 genetics done for the breeder and what can it do ? 

 Still looking at the matter from the standpoint of 



