^'o. 646] 



THE DURATION OF LIFE 



401 



1 day of Drosophila life = .8866 year of human life 

 and 



I year of human life = 1.1279 days of Drosophila life. 



Ill 



We are now in position to make an exact comparison 

 between the life tables of the two organisms. This may 

 be done perhaps most instructively by setting up h lines 

 for the two forms on the basis of age in centiles of the 

 life span, rather than days or years. That is to say, the 

 whole comparable life spans (as defined in this paper) 

 of 97 days in Drosophila and of 86 years for white males 

 will each be divided into 100 equal parts, and the survi- 

 vors at the attainment of the beginning of each centile 

 interval will then be computed. 



This is done for wild-type (long-winged) Drosophila 

 males (Pearl and Parker (27) Life Table II) and male 

 whites in original Eegistration states in 1910 (Grlover's 

 Table 9), in Table 11. 



The two life curves of Table II are shown graphically 

 m Fig. 1, plotted on an arithlog grid. We have, in Table 



II and Fig. 1, for the first time, so far as I am aware, a 

 precise quantitative comparison of the life spans and one 

 of the mathematical functions of the mortality of two 

 different organisms. 



It will be noted that: 



1. The form of the L distributions is fundamentally 

 the same in both of these organisms over the equivalent 

 life spans. Considering the extreme differences in 

 habits of life, structure, physiology, and environmental 

 stresses and strains in the two cases, this is a truly re- 

 markable result. It seems to me to mean that the fac- 

 tors which determine individual longevity, and differ- 

 ences in this character, are biologically deeply rooted, 

 at least as fundamental, apparently, as the factors which 

 determine the specificity in the morphogenesis of organ- 

 isms, and perhaps even more so. We are accustomed 

 loosely to think that the prime factors in determining 



