396 



THE QUARTERLY REVIEW OF BIOLOGY 



ganization or constitution (presumably a 

 purely physical and chemical thing funda- 

 mentally) and if constitution or organiza- 

 tion is inherited, it follows that duration 

 of life will behave exactly as though it 

 were itself inherited. 



In the experiments here described it 

 would seem that the gene for vestigial, 

 besides affecting the form, size and be- 

 havior of the wings of Drosophila, also 

 influences in and through its effects on 

 the total organization pattern of every 

 fly in which it is present, the duration of 



DENSITY OF POPULATION AND LONGEVITY 



Shall we regard the matter as now set- 

 tled, and conclude that in the genetic 

 constitution of the individual we have the 

 determining cause of its longevity? Be- 

 fore doing so it would seem the part of 

 wisdom to see what effect environmental 

 changes may have upon the duration of 

 life of Drosofhila. We have made many 

 studies in this direction, but within the 

 present time limitations it will be possible 

 to discuss only one environmental factor. 

 This one is the density of population in the 



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Initial Density 

 Fig. 4. Mean Duration op Life of Wild Type Drosophila at Different Densities of Population 



life of that fly. We have measured with 

 considerable exactness and manifoldness 

 what the quantitative effect of this gene 

 is upon duration of life (and, of course, at 

 the same time the effect of its allelomorph, 

 the gene for normal wing), under standard 

 and constant laboratory conditions of 

 feeding, etc. 



The view of the case which has been 

 sketched seems to be in accord with the 

 best current opinion as to the biologi- 

 cal meaning and effect of mutant genes 

 generally. 



universe wherein the individual lives its 

 life; or, to put the case in less technical 

 terminology, the degree of crowding to 

 which the individual fly is subjected by its 

 fellows. 



The story of the effect of density of 

 population upon longevity is such a long 

 and complicated one that it will be im- 

 possible here to do more than touch 

 briefly upon its high points. If one makes 

 up a series of one-ounce vials each con- 

 taining newly hatched flies, in numbers 

 varying from one or two pairs per bottle 



