CERTAIN DEMOGRAPHIC BACKGROUNDS FOR POPULATION STUDIES 299 



curves, reproduced in Figure 92 along with 

 comparable curves for the human species. 

 The latter are added because, as Pearl, 

 Park, and Miner pointed out, there is, coin- 

 cidentally, more confluence between the 

 mortality of Tribolium and man than for 



population. The number of deaths attains 

 its maximum during the middle period; the 

 death rate is highest in old age. To quote 

 from the paper cited, "The fundamental 

 similarity in form of the Tribolium life 

 curves and those for man is evident. The 



1000 



SURVIVORSHIPd ^CURVES 



TRIBOLIUM MALES 



TRIBOLIUM FEMALES 

 WHITE MEN 

 WHITE WOMEN 



DEATH (dx) CURVES 



100 60 20 20 60 100 140 180 220 260 



PERCENTAGE DEVIATION FROM MEAN DURATION OF LIFE 

 Fig. 92. Survivorship, death, and death rate curves for the floiu beetie, Tribolium confusum, 

 compared with those for man. ( From Pearl, Park, and Miner. ) 



any other species for which actuarial data 

 exist. 



In the Tribolium curves proper we see 

 that there is a drop in survivors, or an in- 

 crease in deaths, during the early days of 

 life, a slow tapering off during middle hfe, 

 and then a long and gradual decline of the 



only important difference between them is 

 found in the much greater variation ex- 

 hibited by the death id^) curves in Tribo- 

 lium as compared with the human. The 

 Tribolium 6?^ curves not only have a greater 

 range of variation, but are much flatter over 

 the major portion of their course. Tribolium 



