GROUNDS OF RATIONAL OPTIMISM 



written concerning the probable disappearance, in 

 time not far distant, of disease as an important 

 factor in human life, my concern here is with the 

 all-embracing biological generalization which its 

 discoverer, Herbert Spencer, called the law of mul 

 tiplication. Disease is due either to imperfect 

 adaptation of man to his environment (a term 

 which includes bacilli), or to competition between 

 man and man as is abundantly taught us by the 

 coincidence between the curves of death-rate and 

 overcrowding. Biological theory and actual ob 

 servation, however, teach us that the law of com 

 petition, as stated by Malthus, is only a half-truth. 

 True, in its measure, it certainly is that if the pop 

 ulation increases in geometrical ratio while the 

 means of life increases only in arithmetical ratio, the 

 weakest must go to the wall so true that this state 

 ment suggested to Darwin and Wallace indepen 

 dently the theory of natural selection ; but another 

 truth of equal importance was unrecognized by 

 Malthus. This truth, which immediately abro 

 gates the horribly pessimistic inference from the 

 Malthusian proposition, is that the population 

 does not increase in geometrical ratio, but that 

 its rate of increase constantly tends, with the 

 development of the individual organism, to di 

 minish. In other words, the higher the organism, 

 the lower the birth-rate. This is a fact demonstra 

 ble not only a priori, by consideration of the fact 

 that if the individual expends more energy upon 

 his own individualization he has less to expend 



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