The Biology of Senescence 



'When we refer to sidereal time as being the canvas on which 

 the pattern of our existence is spread, we notice that the time 

 needed to effectuate a certain unit of physiological work of 

 repair is about four times greater at fifty than at ten years of 

 age. Everything, therefore, occurs as if sidereal time flowed four 

 times faster for a man of fifty than for a child often. It is evi- 

 dent, on the other hand, that from a psychological point of 

 view many more things happen to a child in a year than to an 

 old man. The year therefore seems much longer to the child. . . . 

 Thus we find that when we take physiological time as a unit of 

 comparison, physical time no longer flows uniformly. This 

 affirmation revolts one if the words are taken in a literal sense. 

 But . . . the expression "flow of time" ... is entirely false and 

 does not correspond to a reality. When ... we say that physical 

 time measured by means of a unit borrowed from our physio- 

 logical time no longer flows uniformly, it simply means that it 

 does not seem to flow uniformly . . . Must one consider this fact 

 as the indication of a difference of magnitude between our 

 short individual period and the immense periods of the uni- 

 verse? Must we see a proof of the existence of such periods? 

 Who knows? All that we can say at present is that our crude 

 language, lacking appropriate words, translate this knowledge 

 into improper, inadequate expressions such as "There are two 

 species of time" or "Physiological time does not flow uniformly 

 like physical time" . . . We must not let ourselves be duped 

 by these words, etc. . . .' 



It is startling how many distinguished biologists have sub- 

 sequently quoted the notion of a distinct 'biological* time with 

 apparent sanction. The alcoholic who draws on his bottle 

 irregularly will find that its progress towards emptiness follows 

 an irregular scale, 'alcoholic time', so that judged by the rate 

 of emptying of the bottle, 'sidereal' time appears to progress 

 unevenly. But variation in rate is hardly an occult, or even an 

 unfamiliar, phenomenon. Like others before him, du Notiy has 

 gone down clutching a platitude and come up embracing a 

 metaphysical system. 



In almost any other important biological field than that of 

 senescence, it is possible to present the main theories historic- 



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