THE GREAT RELAY RACE 435 



principle of continuous inheritance, although not always recognized, 

 has been used and practiced as an art from the begiiuiing, not only in 

 the case of man himself, but also with domestic animals and cultivated 

 plants. The real factors of heredity, however, together with the 

 orderly "laws" which indicate their manner of working, have not 

 been analyzed and made into a science until within comparatively 

 recent times. The very word "genetics" was first employed by 

 Bateson in 1906. 



To agree in advance to conduct any would-be excursionist down the 

 rapidly flowing genetic river to a definite landing place is both pre- 

 sumptuous and unwise, for there are at present too many long, un- 

 charted stretches and too much that is unknown to make positive 

 textbook promises of this kind probable of fulfillment. Nevertheless, 

 the general direction in which the river of genetics flows, in spite of 

 its shifting changes, is plain to all, and the tales of returning travelers 

 invite us to intellectual adventure. Students in this field today, 

 however, must make up their minds at the start to be alert explorers 

 and ambitious pioneers, rather than passive, personally conducted 

 excursionists. 



Seed and Soil 



In the relay race of heredity the continuous thing that is handed on 

 from generation to generation is not the lighted torch, but rather 

 something that corresponds to a box of matches with which another 

 torch may be lighted. Biological inheritance, unlike legal inheritance 

 by which material possessions are transferred from parents to children, 

 consists in the transmission of genes, or ultra-microscopic chemical 

 units possessing the uncanny capacity, under suitable conditions, of 

 expanding into visible structures or traits that resemble those in the 

 parental make-up. 



Heredity binds the generations together and is absolutely essential, 

 but in itself it is not enough. The potent genes, which are the 

 determiners of heredity, must have a suitable setting in which to 

 unfold their potentialities. This necessary setting is called the 

 environment. It expresses and represents the spread that occurs 

 within the Hmits of the hereditary possibilities, for the hereditary 

 pattern may be enhanced or dwarfed in its expression by the action 

 of the environment. Stated another way, the environment does not 

 change the quality of hereditary characters, although it makes possible 

 either a greater or a lesser development of them. 



