PREFACE, 



Looking forward to the hope that the human 

 race may become consciously and increasingly 

 master of itself and of its destiny, and re- 

 cognizing the Darwinian principle of the selection 

 of the fittest as the only means of preventing the 

 moral and physical degeneracy which, like an in- 

 ternal dry rot, has hitherto been the besetting 

 danger of all civilizations, I desire that the 

 thinkers who mould the opinions of mankind shall 

 not be led astray from the true path of enduring 

 progress and happiness by reliance on fallacious 

 beliefs which will not bear examination. Such, at 

 least, is the feeling or motive which has prompted 

 me to devote much time and thought to a difficult 

 but important inquiry in a debatable region of 

 inference and conjecture, where (I am afraid) 

 evidence on either side can never be absolutely 

 conclusive, and where, especially, the absolute 

 demonstration of a universal negative cannot 

 reasonably be expected. 



