The Distribution of Senescence 



Zoo, by kind permission of the Director, and Fig. 13 from data 

 sent me by Miss D. Gardner. 



Maximum longevity records of animals species have a 

 definite, but limited, use in giving a comparative picture of the 

 possible longevity in different forms. They can give no direct 

 evidence of the distribution of senescence, but they can provide 

 an important test of a number of general theories — those based, 

 for example, on the exhaustion of neurones (Vogt and Vogt, 

 1946; Bab, 1948) are difficult to reconcile with the variation 

 in specific age and potential longevity between closely-related 

 forms. A large scatter of maximum recorded ages is in itself 

 suggestive, but not of course demonstrative, evidence of an 

 indeterminate life-span, except in cases where it is evidence only 

 of improving cultural methods and better understanding of the 

 requirements of the animal under laboratory or domestic con- 

 ditions. For a very large range of species we can readily infer 

 a 'potential' age which is never attained, either in the wild, 

 because of accident and predation, or in captivity, because the 

 animals cannot be kept alive in captivity — the 'potential' 

 longevity of snakes, chamaeleons (Flower, 1925, 1937) or 

 mammals of little known habits (pangolins — Flower, 1931) are 

 cases in point. 'Concerning the length and brevity of life in 

 beasts, the knowledge which may be had is slender, the obser- 

 vation negligent, and tradition fabulous; in household beasts the 

 idle life corrupts; in wild, the violence of the climate cuts them 

 off' (Historia Vitae et Mortis). With most birds, fully domestic 

 mammals, hardy reptiles such as tortoises, and man, however, 

 maximum records can be taken to represent in some real degree 

 the extreme length of time for which the species, or its hardier 

 genotypes, can remain self-maintaining if protected from gross 

 disease or accident. Theories of senescence must fit these data, 

 or at least not contradict them, to be available as working 

 hypotheses. 



2-2 Maximum Longevities in Animals 



Apart from the observations collected by Bacon, which were 

 remarkably critical and accurate compared with the wildness of 

 later estimates, the accurate study of animal life-spans virtually 



45 



