2 Introduction 



limited, special fields. It may be appropriate to insert a telling quota- 

 tion from a theoretical physicist (Whittaker, 1952). 



"At this point it may be observed that there is a notable difference 

 between theoretical Physics on the one hand and Pure Mathematics 

 and Experimental Physics on the other, in respect of the enduring 

 validity of the advances that are made. A theorem of Pure Mathe- 

 matics, once discovered, is true forever; all the pure mathematics that 

 Archimedes knew more than 2000 years ago is taught without essential 

 change to our students today. And the results of Experimental Physics, 

 so far as they are simply the expression in mathematical language of 

 the unchangeable brute facts of experience, have the same character 

 of permanence. The situation is different with an intellectual adven- 

 ture such as Theoretical Physics: it is built round conceptions and the 

 progress of the subject consists very largely in replacing these con- 

 ceptions by other conceptions, which transcend, or even contradict, 

 them. At the beginning of the century the two theories which seemed 

 most firmly established were that which represented gravitation in 

 terms of action at a distance, and that which represented light as a 

 motion of waves: and we have seen the one in a certain sense sup- 

 planted by General Relativity and the other trying to make the best 

 of an uneasy conjunction with Quantum-mechanics. The fame of a 

 theoretical physicist rests on the part that his ideas have played in the 

 history of the science; it does not necessarily detract from his impor- 

 tance if none of them survive into the physics of his remote suc- 

 cessors." 



Genetics, younger than other biological fields, has not reached the 

 level at which theoretical genetics can be established as a recognized 

 discipline. Generalizing and theorizing in genetics is still a part, and 

 a minor one, of the factual attack upon individual problems, though 

 it seems that the tendency is increasingly to extend specific generaliza- 

 tions to a wider field, which would amount to the emergence of a 

 theoretical genetics. Thus my endeavor to sketch an outline of a future 

 theoretical genetics is not outside the trends of the time. Speaking for 

 myself, it is actually a further development of a personal inclination 

 which has been at the back of about forty-five years of genetical work. 

 Though I had the good fortune to contribute a large and diversified 

 mass of factual data in many separate fields of our science, I always 

 made the effort to draw general conclusions and to extend these to as 

 many groups of facts as I could muster. To satisfy my own need for 

 unified thought, I tried to work generalized, all-embracing ideas into 

 a unified and coordinated system which might be called genetical 



