THE PHYSICAL BASIS OF 

 HEREDITY 



CHAPTER I 



INTRODUCTION 



That the fundamental aspects of heredity should have 

 turned out to be so extraordinarily simple supports us in 

 the hope that nature may, after all, be entirely approach- 

 able. Her much-advertised inscrutability has once more 

 been found to be an illusion due to our ignorance. This 

 is encouraging, for, if the world in which we live were as 

 complicated as some of our friends would have us believe 

 we might well despair that biology could ever become an 

 exact science. Personally I have no sympathy with the 

 statement that ''the problem of the method of evolution 

 is one which the biologist finds it impossible to leave alone, 

 although the longer he works at it, the farther its solution 

 fades into the distance. ^ ' On the contrary, the evidence 

 of recent years and the methods by means of which this 

 evidence is obtained have already in a reasonably short 

 time brought us nearer to a solution of some of the import- 

 ant problems of evolution than seemed possible only a few 

 years ago. That new problems and developments have 

 arisen in the course of the work — as they are bound to 

 do in any progressive science, as they do in chemistry and 

 in physics for example — goes without saying, but only a 

 spirit of obscurantism could pretend that progress of this 

 kind means that we see the solution of our problem fading 

 away into the distance. 



Mendel left his conclusions in the form of two general 

 laws that may be called the law of segregation and the 



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