CHAPTER VII 



EXPERIMENTAL STUDIES ON THE DURATION 



OF LIFE 



INHEKITANCE OF DURATION OF LIFE IN DROSOPHILA 



IN the last chapter there was presented indubitable 

 proof that inheritance is a major factor in determining 

 the duration of life in man. The evidence, while entirely 

 convincing and indeed in the writer's opinion critically 

 conclusive, must be, in the nature of the case, statistical 

 in its nature. Experimental inquiries into the duration 

 of human life are obviously impossible. It is always 

 important, however, as a general principle, and particu- 

 larly so in the present instance, to check one's statistical 

 conclusions by independent experimental evidence. This 

 can be successfully done, when one's problem is longevity, 

 only by choosing an animal whose life-span relative to 

 that of man is a short one, and in general the briefer it 

 is, the better suited will the animal be for the purpose. 



An organism which rather completely fulfils the re- 

 quirements of the case, not only in respect of the short- 

 ness of the life span, but also in other ways, such as 

 ease of handling, feeding, housing, etc., is the common 

 "fruit" or "vinegar" fly, Drosophila melanogaster. 

 This insect, which every one has seen hovering about 

 bananas and other fruit in fruit shops, has lately attained 

 great fame and respectability as a laboratory animal, 

 as a result of the brilliant and extended investigations 

 of Morgan and his students upon it, in an analysis of the 

 mechanism of heredity. DrosopMa is a small fly, per- 



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