24 THE DUKATION OF LIFE. 



time, a supposition which is of course hardly conceivable. The 

 individual would nevertheless be unable to avoid, from time to 

 time, slight injuries to one or another part of its body. The 

 injured parts could not regain their former integrity, and thus the 

 longer the individual lived, the more defective and crippled it 

 would become, and the less perfectly would it fulfil the purpose of 

 its species. Individuals are injured by the operation of external 

 forces, and for this reason alone it is necessary that new and perfect 

 individuals should continually arise and take their place, and this 

 necessity would remain even if the individuals possessed the power 

 of living eternally. 



From this follows, on the one hand, the necessity of reproduction, 

 and, on the other, the utility of death. Worn-out individuals are 

 not only valueless to the species, but they are even harmful, for 

 they take the place of those which are sound. Hence by the 

 operation of natural selection, the life of our hypothetically im- 

 mortal individual would be shortened by the amount which was 

 useless to the species. It would be reduced to a length which 

 would afford the most favourable conditions for the existence of as 

 large a number as possible of vigorous individuals, at the same 

 time. 



If by these considerations death is shown to be a beneficial 

 occurrence, it by no means follows that it is to be solely accounted 

 for on grounds of utility. Death might also depend upon causes 

 which lie in the nature of life itself. The floating of ice upon 

 water seems to us to be a useful arrangement, although the fact 

 that it does float depends upon its molecular structure and not 

 upon the fact that its doing so is of any advantage to us. In like 

 manner the necessity of death has been hitherto explained as due to 

 causes which are inherent in organic nature, and not to the fact 

 that it may be advantageous. 



I do not however believe in the validity of this explanation ; 

 I consider that death is not a primary necessity, but that it has 

 been secondarily acquired as an adaptation. I believe that life is 

 endowed with a fixed duration, not because it is contrary to its 

 nature to be unlimited, but because the unlimited existence of 

 individuals would be a luxury without any corresponding advantage. 

 The above-mentioned hypothesis upon the origin and necessity of 

 death leads me to believe that the organism did not finally 



