312 DARWINISM AND THE PROBLEMS OF LIFE 



be called immortal, because no part of their body 

 perishes without providing a substitute ; in other words, 

 no part forms a corpse. 



We know too little of the biogens and their activity 

 to be able to say why all biogens are not indefatigable 

 in creating a substitute. It has been suggested that the 

 temporary biogens can only achieve this by drawing on 

 their own energy. They differ so much in the structure 

 of their elements that some irregularity is unavoidable 

 in the co-operation of the various parts. In the course 

 of their life these irregularities increase, and at last a 

 time must come when the biogens are shaken to the 

 foundations of their structure. They then break up. 

 That is the meaning of death. 



We are led to conclude, then, that the introduction of 

 death into the world was useful, because the living 

 matter was bound to give up all claim to eternal con- 

 tinuity before it could be so differentiated that its 

 possessor could escape violent death. However, some 

 of the biogens had to retain the power of continuous 

 creation, in order to maintain life upon the earth. 



Just as death was introduced by natural selection, so 

 the moment of its occurrence is carefully regulated. In 

 each animal species natural death only sets in when the 

 maintenance of the species is secured. The duration 

 of life is strictly proportioned in all organisms to their 

 reproductive powers. But I have not space to discuss 

 this in detail here. 



Life will not continue for ever on the earth. A time 

 will come when the earth will course through space, 

 a frozen mass, and a violent end will come to all 



