EVOLUTION AND MORTALITY 



By 

 RAYMOND PEARL 



Institute for Biological Research, Johns Hopkins University 



THE PROBLEM 



' N 1910, in an attempt to approach 

 the problem of human mortality 

 from a more rational standpoint 

 than that of current vital statistics, 

 I (8) discussed the distribution of human 

 deaths on the basis of an organological 

 classification of the several statistically 

 recorded causes. The underlying idea in 

 the classification was to group all causes 

 of death under the heads of the several 

 organ systems of the body, the functional 

 breakdown of which is the immediate or 

 predominant cause of the cessation of life. 

 The basis of the classification was not that 

 of etiology, but rather that of the anatom- 

 ical location of the principal breakdown. 

 The matter was further discussed and the 

 original classification amended and cor- 

 rected in later publications (9, 10). 



In these investigations there came to 

 light evidence that the present character- 

 istics and distribution of human mortality 

 are in part — perhaps a considerable part — 

 the results or consequences of the evolu- 

 tionary history of the human body itself. 

 It appeared that the different organ sys- 

 tems of the body are not all equally cap- 

 able of withstanding the environmental 

 stresses and strains which they have to 

 meet. The evidence on this point was 

 necessarily suggestive rather than con- 

 clusive. Human vital statistics, taken 

 by themselves, are for many reasons in- 

 adequate to elucidate such a point as this. 



It demands a study of the evolutionary 

 progression which has occurred in respect 

 of mortality among the animals lower in 

 the scale than man, who represents only 

 the final end term in the series. The real 

 question, on which we should like to have 

 evidence is: How do the relative mortal- 

 ities chargeable to breakdown of each of 

 the different organ systems of the body 

 compare among the different orders of 

 animals, including man? 



What obviously is needed to answer the 

 question is a record of the comparative 

 pathological anatomy of the different 

 orders of vertebrate animals. Unfortu- 

 nately there does not exist anything like 

 a complete or detailed body of knowledge 

 regarding the pathology of wild verte- 

 brate animals living in a natural state. 

 There are several reasons for this lack, 

 besides the obvious one that few persons 

 have particularly interested themselves 

 in such study. The wild animals that 

 happen to be killed by hunters are the 

 survivors of a steady process of natural 

 selection, and are therefore apt to be in 

 an excellent state of health. The sick, 

 weak and defective have long since died 

 off, under circumstances practically always 

 making impossible post-mortem exam- 

 ination. Again wild animals probably 

 only rarely die a natural death due to 

 internal pathological changes. When an 

 animal in a state of nature falls appreci- 

 ably below par in health, sooner or later 

 something kills it. 



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