EXPEEIMENTAL STUDIES ON THE DUEATION 

 OF LIFE. IV. DATA ON THE INFLUENCE 

 OF DENSITY OF POPULATION ON 

 DUEATION OF LIFE IN 

 DROSOPHILA 1 



PEOFESSOE EAYMOND PEAEL AND SYLVIA L. PAEKER 



Faiely early in our experimental work on duration of 

 life in Drosophila it became apparent to us that the num- 

 ber of flies per bottle, or, since the bottles used are of 

 uniform size, the density of population, had some influ- 

 ence on the mean duration of life of the flies, when other 

 environmental conditions are constant. Such a relation- 

 ship might reasonably be expected a priori, from what 

 is known of the influence of this factor on human death 

 rates, commonly expressed as Farr's Law {cf. Farr, W. 

 (35), Brownlee, J. (36, 37)), and on other biological func- 

 tions, such as growth (Semper, K. (38), Bilski, F. (39)), 

 resistance to poisons (Drzwina and Bohn (40)), rate of 

 reproduction (Pearl and Surface (41), Pearl and Parker 

 (42)), etc. As soon as it was recognized that this vari- 

 able, density of population, might influence our experi- 

 mental results with Drosophila, care was taken in setting 

 up experiments to make this a constant in each case. At 

 the same time the records of the earlier work were care- 

 fully re-examined to determine what part this variable 

 may have played in the results. Happily it was found 

 that in none of our work so far published upon the dura- 

 tion of life in Drosophila had density of population 

 varied enough to have any appreciable effect upon the 

 results or conclusions. 



As was recently pointed out by Pearl and Parker (42), 

 however, "there can be no question that this whole 

 matter of influence of density of population, in all senses, 

 upon biological phenomena, deserves a great deal more 



1 Papers from the Department of Biometry and Vital Statistics, School 

 of Hygiene and Public Health, Johns Hopkins University. No. 63. 

 312 



