THE COMPARATIVE BIOLOGY OF AGEING: 

 A PHYSIOLOGICAL APPROACH 



Francois Bourliere 



Centre de Gerontologie Claude Bernard, and 

 Laboratoire de Physiologie, Faculte de Medicine, Paris 



Physiological changes occurring after maturity have been 

 mainly studied in man and a few laboratory mammals, such 

 as rats, mice and guinea pigs. The main results of these inves- 

 tigations have been reviewed elsewhere and another summary 

 would seem to be superfluous. It is sufficient to say that most 

 of these changes lead to a decrease in viability and an increase 

 in vulnerability of the organism. The morphological and 

 functional involution which characterizes ageing starts in the 

 various organs at varying periods early in life. Its end-result 

 at the organismic level is always a decreased adaptation to the 

 environmental conditions. 



But senescence is not limited to mammals, and one may 

 wonder if the ageing patterns of lower vertebrates and inverte- 

 brates are altogether similar to that of man and his laboratory 

 animals. To be sure, our knowledge of the ageing processes in 

 the various types of animals is hardly more than sketchy, but 

 some comparisons are nevertheless possible. We have, for 

 instance, some indications of the influence of age on fertility 

 of various warm-blooded and cold-blooded vertebrates. In 

 the rat, the number of young per litter is maximal at the 

 second or third litter and decreases regularly afterwards 

 (King, 1924). In guinea pigs, the greatest fertility coincides 

 with early maturity (211-420 days) and then diminishes 

 (Rogers, 1951). The highest egg production in fowls, as shown 

 in Fig. 1, is observed in young birds, and the number of eggs 

 laid annually decreases regularly as females grow older 

 (Romanoff and Romanoff, 1949). 



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