THE GREAT RELAY RACE 441 



and duration, to be of general significance in establishing the laws of 

 inheritance. Not only would any such ambitious program take too 

 many generations to reach any satisfactory conclusions, even if it 

 were possible, but also it would involve too many insuperable social 

 diflSculties. In the case of mankind, therefore, we are forced to 

 resort to experiments in marriage and other sexual relations that have 

 already been made in the past, for collecting data, and this type of 

 investigation demands the technique of statistical treatment. 



The third method of approach in storming the citadel of genetics is 

 the ex'perimental method. This has proven to be very successful. By 

 controlling breeding of animals and plants and observing the outcome, 

 which is not open to the objections encountered when human material 

 is employed, it has become possible to find out much concerning the 

 modus operandi of inheritance. The same biological laws and pro- 

 cedures that are found to be true of plants or animals may then, to a 

 large extent at least, be applied to man. This method will be elabo- 

 rated somewhat in the following sections. 



All of these methods, namely, observation, statistical treatment, 

 and experimental breeding, are concerned primarily wnth somato- 

 plasms. The germplasmal method of approach, on the other hand, is 

 concerned with the concealed beginnings of the life story, rather than 

 with its visible sequel in the bodies of organisms. The germplasmal 

 approach has to do wdtli the astonishing behavior of the genes, which 

 are the determiners of subsequent somatoplasmal manifestations. 

 This underground phase of the heredity problem is proving in recent 

 years to be most illuminating, and some consideration of it, together 

 with the experimental method just mentioned, will make up the 

 essential remaining part of this section on genetics. 



The Experimental Method 



The Usefulness of Hybrids 



In order to learn the secrets of inheritance by the controlled crossing 

 of plants and animals, it is necessary to use parental stocks that differ 

 from each other in some of their characteristics. When this is done, 

 hybrids are produced in which the respective contributions to the 

 offspring from the two parents may be determined, and thus the 

 first steps made in the analysis of the problems of inheritance. 



If both parents and the consequent offspring are alike, then a color- 

 less monotony results that gives no differential clue as to how heredity 



