The Biology of Senescence 



that it is not there. The amount of material on which such a 

 foundation could be built has increased, though not very 

 rapidly, during the present century. Its quantity is still inversely 

 proportional to the importance of the subject. 



There are not many adequate reviews of the modern bio- 

 logical literature. The most recent are those of Lansing ( 1 95 1 , 52) . 

 A previous review of mine contains little which is not repeated 

 here (Comfort, 1954). Some of the more celebrated 'general 

 theories' have received spirited treatment in a review by 

 Medawar (1945). The literature of animal population statistics 

 has been reviewed by Deevey (1947) and that of invertebrate 

 senescence by Szabo (1935) and by Harms (1949). It is a 

 pleasure to acknowledge my indebtedness to these reviews and 

 to the bibliography of Shock (1951). A great deal of clinico- 

 pathological material upon the age-incidence of various human 

 diseases and the weights of organs throughout life has been col- 

 lected by Burger (1954). In a depressingly large number of 

 fields, there has been little new information in the last twenty 

 years. Other reviews of specific topics will be cited in their 

 place. The senescence of plants is not discussed here: it has been 

 reviewed in some detail by Crocker (1939), to whose paper 

 there seems little to add. 



Senescence is probably best regarded as a general title for the 

 v group of effects which, in various phyla, lead to a decreasing 

 expectation of life with increasing age. It is not, in this sense, a 

 'fundamental', 'inherent', or otherwise generalizable process, 

 and attempts to find one underlying cellular property which 

 explains all instances of such a change are probably misplaced. 

 It is important and desirable to recognize the origins of many 

 such general theories, which owe much to folk-lore on one 

 hand and to the emotional make-up of their authors on the 

 other. The demoralizing effect of the subject of senescence, even 

 upon biologists of the highest competence and critical intel- 

 ligence, is well illustrated by the following passage from Pearl 

 (1928), the father of animal actuarial studies: 



'(Somatic death in metazoa) is simply the price they pay for 

 the privilege of enjoying those higher specializations of structure 

 and function which have been added on as a sideline to the 



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