EVOLUTION AND MORTALITY 



2-77 



This is obviously a biologically improb- 

 able assumption, but limiting assumptions 

 often are highly improbable. 

 II. The second assumption is that 



No X = VI 



that is, that no death now in Class X was 

 due to lesions of the alimentary tract or 

 its associated organs. This again is a 

 highly improbable assumption, but it is 

 limiting. 



The resultant effect of redistributing 

 the proportionate mortality according to 

 these two assumptions, together with the 



TABLE 3 



The proportionate mortality assigned to breakdown of the 



alimentary tract and its associated organs, under 



each of three assumptions 



ANIMAL GROUP 



Reptiles 



Birds 



Mammals 



Man, Sao Paulo 



Man, England and 

 Wales 





XIS 





Random 



ASSUMP- 



SAMPLE 



TION 



or ALL 



I 



DEATHS. 



ALLX =VI 



(.DATA 





FROM 





TABLE 2.) 



fir cent 



fir cmt 



77-6 



58.6 



63.5 



50.83 



5J-5 



38.66 



43-3 



39 • «. 



2.9. 8 



11.40 



ASSUMP- 

 TION 



3*- 7 



37.8 

 30.6 

 36.9 



19. 1 



initial assumption of random distribution 

 of the deaths in Class X, which underlies 

 table z, is shown in table 3 . 



In order to make clearer the significance 

 of the data of table 3, figure z has been 

 prepared. 



It is seen that the trend of the mortality 

 under Assumption II is, as a whole, 

 slightly downward if man in England and 

 Wales be taken into account. Leaving 

 this last point out of consideration the 

 trend under Assumption II is nearly hori- 

 zontal. But under the limiting Assump- 

 tion I the trend is plainly downward. 

 The true facts must fall somewhere be- 



tween I and II. Hence the conclusion 

 seems to be that, however the unassign- 

 able mortality of Class X may be supposed 

 to be distributed, there has been a steadily 

 decreasing proportion of the total mortal- 

 ity due to breakdown of the alimentary 

 tract during the evolutionary progression 

 from reptiles to man. 



The limiting assumptions were applied 

 in the same way to the mortality from 

 breakdown of the respiratory system, with 



Sept. Bird. Mamm. SJ> E.&W. 



Fig. i. Trend ox the Mortality Assigned to 

 Class VI, under Three Assumptions 



the similar result of showing that the 

 evolutionary trend of the mortality as- 

 signable to this system has been, in greater 

 or smaller degree, in the direction indicated 

 in table z. 



It would seem, then, that even though 

 the anatomically unassignable mortality 

 in the London Zoological Garden material 

 is absolutely larger than is desirable, still 

 the element of uncertainty that is thereby 

 introduced into our conclusions pertains 



