PROBLEMS OF GENETICS 



CHAPTER I 



INTRODUCTORY 



The purpose of these lectures is to discuss some of the 

 familiar phenomena of biology in the light of modern discoveries. 

 In the last decade of the nineteenth century many of us per- 

 ceived that if any serious advance was to be made with the group 

 of problems generally spoken of as the Theory of Evolution, 

 methods of investigation must be devised and applied of a kind 

 more direct and more penetrating than those which after the 

 general acceptance of the Darwinian views had been deemed 

 adequate. Such methods obviously were to be found in a 

 critical and exhaustive study of the facts of variation and heredity, 

 upon which all conceptions of evolution are based. To construct 

 a true synthetic theory of Evolution it was necessary that vari- 

 ation and heredity instead of being merely postulated as axioms 

 should be minutely examined as phenomena. Such a study 

 Darwin himself had indeed tentatively begun, but work of a 

 more thorough and comprehensive quality was required. In 

 the conventional view which the orthodoxy of the day prescribed, 

 the terms variation and heredity stood for processes so vague 

 and indefinite that no analytical investigation of them could be 

 contemplated. So soon, however, as systematic inquiry into 

 the natural facts was begun it was at once found that the ac- 

 cepted ideas of variation were unfounded. Variation was seen 

 very frequently to be a definite and specific phenomenon, af- 

 fecting different forms of life in different ways, but in all its 

 diversity showing manifold and often obvious indications of 

 regularity. This observation was not in its essence novel. 

 Several examples of definite variation had been well known to 



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