INTRODUCTION 5 



between father and son, as well as that which often 

 appears between nephew and uncle or even more 

 remote relatives, is due not to a direct entail of the 

 characteristics in question, but to the fact that the 

 characteristics are "based on descent" from a 

 common source. In other words, an *' hereditary 

 character" of any kind is not an entity or unit which 

 is handed down from generation to generation, but 

 is rather a method of reaction of the organism to the 

 constellation of external environmental factors under 

 which the organism lives. 



To unravel the golden threads of inheritance 

 which have bound us all together in the past, as 

 well as to learn how to weave upon the loom of the 

 future, not only those old patterns in plants and 

 animals and men which have already proven worth 

 while, but also to create new organic designs of an 

 excellence hitherto impossible or undreamed of, is 

 the inspiring task before the geneticist to-day. 



3. The Maintenance of Life 



So far as we know, every living thing on the earth 

 to-day has arisen from some preceding form of life. 



How the first spark of life began will probably 

 always be a matter of pure speculation. Whether 

 the beginnings of what is called life came through 

 space from other worlds on meteoric wings, as Lord 

 Kelvin has suggested ; whether it was spontaneously 

 generated on the spot out of lifeless components ; 

 or whether life itself was the original condition of 



