442 THE WONDER OF LIFE 



vigorous and wholesome. As Goethe said, ' Death is her 

 expert device to get plenty of life.' 



Summary. There is, as we have hinted, reason to 

 believe that natural death is not to be regarded simply as 

 an intrinsic necessity the fate of all life ; we can carry 

 the analysis further, and say that it is incident on the com- 

 plexity of the bodily machinery, which makes complete 

 recuperation wellnigh impossible, and almost forces the 

 organism to accumulate arrears, to go into debt to itself ; 

 that it is incident on the limits which are set to the multi- 

 plication and renewal of cells within the body, thus nerve- 

 cells in higher animals cannot be added to after an early 

 stage in development ; that it is incident on the occurrence 

 of organically expensive modes of reproduction, for repro- 

 duction is often the beginning of death. At the same time, 

 it seems difficult to rest satisfied with these and other 

 physiological reasons, and we fall back on the selectionist 

 view that the duration of life has been, in part at least, 

 punctuated from without and in reference to large issues ; 

 it has been gradually regulated in adaptation to the welfare 

 of the species. 



As we have suggested in The Biology of the Seasons, 

 several groups should be distinguished. (1 ) The first is that 

 of the immortal unicellular animals which never grow old, 

 which seem exempt from natural death. (2) The second 

 is that of many animals which reach the length of their 

 life's tether without any hint of ageing and pass off the 

 scene or are shoved off victims of violent death. In 

 many fishes and reptiles, for instance, which are old in years, 

 there is not in their organs or tissues the least hint of age- 

 degeneration. (3) The third is that of the majority of 

 civilized human beings, some domesticated and some wild 



